<![CDATA[Curl Global Community - Try 5: Reading Our Score Data]]> https://communities.curl.com/ Fri, 01 May 2026 20:43:02 +0000 MyBB <![CDATA[Page 8: Extra Practice]]> https://communities.curl.com/showthread.php?tid=78 Mon, 20 Jun 2011 04:34:06 +0000 https://communities.curl.com/showthread.php?tid=78 Extra Practice

Practice Problem 1: Basics

Let’s write a program that writes the data displayed by RecordGrid into a file. The program must satisfy the following requirements:
  • The location to which the file is saved is to be specified by the user, using the Save as dialog box.
  • The data displayed using RecordGrid will have three fields: name, age, and score.
  • The overwriting of data in an existing file shall be prohibited.


Hint: Use commas to delimit each of the fields of the data in each Record, and then write each Record to one line of the file.

Solution

Solution Program: c:\Curl\Try5\04_exercise1\start.curl

Code:
{value
    let out:#TextOutputStream
    let data:RecordSet = {RecordSet
                             {RecordFields
                                 {RecordField name, domain = String},
                                 {RecordField age, domain = int},
                                 {RecordField score, domain = int}
                             },
                             {RecordData name = Matt, age = 33, score = 88},
                             {RecordData name = Sarah, age = 27, score = 79},
                             {RecordData name = Jacob, age = 26, score = 90}
                         }
    
    let cb:CommandButton = {CommandButton
                               label = Save,
                               {on Action do
                                   {if-non-null loc = {choose-file style = save-as} then
                                       {try
                                           set out = {write-open
                                                         error-if-exists? = true,
                                                         loc
                                                     }
                                           {for r:Record in data do
                                               {out.write-one-string
                                                   {format "%s , %s, %s \r\n,
                                                       r[name], r[age], r[score]}
                                               }
                                           }
                                        catch e:IOException do
                                           {popup-message Error writing data"}
                                           {output e.message}
                                        finally
                                           {if-non-null out then
                                               {out.close}
                                           }
                                       }
                                   }
                               }
                           }
    {VBox
        {RecordGrid
            record-source = data,
            width = 10cm,
            height = 3cm
        },
        cb
    }
}

Explanation

RecordSets, like arrays, are collections, so a RecordSet can be passed to a for loop, which will process the contained Records in order.
]]> Extra Practice

Practice Problem 1: Basics

Let’s write a program that writes the data displayed by RecordGrid into a file. The program must satisfy the following requirements:
  • The location to which the file is saved is to be specified by the user, using the Save as dialog box.
  • The data displayed using RecordGrid will have three fields: name, age, and score.
  • The overwriting of data in an existing file shall be prohibited.


Hint: Use commas to delimit each of the fields of the data in each Record, and then write each Record to one line of the file.

Solution

Solution Program: c:\Curl\Try5\04_exercise1\start.curl

Code:
{value
    let out:#TextOutputStream
    let data:RecordSet = {RecordSet
                             {RecordFields
                                 {RecordField name, domain = String},
                                 {RecordField age, domain = int},
                                 {RecordField score, domain = int}
                             },
                             {RecordData name = Matt, age = 33, score = 88},
                             {RecordData name = Sarah, age = 27, score = 79},
                             {RecordData name = Jacob, age = 26, score = 90}
                         }
    
    let cb:CommandButton = {CommandButton
                               label = Save,
                               {on Action do
                                   {if-non-null loc = {choose-file style = save-as} then
                                       {try
                                           set out = {write-open
                                                         error-if-exists? = true,
                                                         loc
                                                     }
                                           {for r:Record in data do
                                               {out.write-one-string
                                                   {format "%s , %s, %s \r\n,
                                                       r[name], r[age], r[score]}
                                               }
                                           }
                                        catch e:IOException do
                                           {popup-message Error writing data"}
                                           {output e.message}
                                        finally
                                           {if-non-null out then
                                               {out.close}
                                           }
                                       }
                                   }
                               }
                           }
    {VBox
        {RecordGrid
            record-source = data,
            width = 10cm,
            height = 3cm
        },
        cb
    }
}

Explanation

RecordSets, like arrays, are collections, so a RecordSet can be passed to a for loop, which will process the contained Records in order.
]]> <![CDATA[Page 7: Summary]]> https://communities.curl.com/showthread.php?tid=77 Mon, 20 Jun 2011 04:23:25 +0000 https://communities.curl.com/showthread.php?tid=77 TRY 5 Summary

Reading and writing data from/to a file

Step 1. Specifying the location of a file

Code:
let location_variable_name:Url = {url “path to file location”}

Step 2. Opening file as a Stream

  • TextInputStream (read)
  • TextOutputStream (write)

Code:
let stream_variable_name:TextInputStream = {read-open location_variable_name}
let stream_variable_name:TextOutputStream = {write-open location_variable_name}

Step 3. Using methods to read or write data
  • Methods such as read-line or write-one-string

Step 4. Closing the file

Code:
{if-non-null stream_variable_name then
    {stream_variable_name.close}
}

Repeat Expressions

until expression (processing repeats until conditional expression is true)

Code:
{until conditional_expression do
    body
}

for expression (specifying a range)

Code:
{for repeat variable:int = initial_value to final_value step step_size value do
    body
}

As well as to, there are also the below, downto, and above keywords. The step_size can be omitted when the desired step_size is 1.

for expression (repeats only the values among the elements of a collection, such as an array)

Code:
{for element_variable:element_type key key_variable[:key type] in (collection) name do
    processing
}

Note that element_variable:Element_type or key key_variable: key_type can be omitted.

Exception Processing

Code:
{try
    Processing in which an exception may occur.
catch exception_variable_name: exception
    Exception Processing
finally
    Processing that must be performed regardless of whether an exception occurs
}

The catch and finally clauses can be omitted. Also, each try can be declared more than once.]]> TRY 5 Summary

Reading and writing data from/to a file

Step 1. Specifying the location of a file

Code:
let location_variable_name:Url = {url “path to file location”}

Step 2. Opening file as a Stream

  • TextInputStream (read)
  • TextOutputStream (write)

Code:
let stream_variable_name:TextInputStream = {read-open location_variable_name}
let stream_variable_name:TextOutputStream = {write-open location_variable_name}

Step 3. Using methods to read or write data
  • Methods such as read-line or write-one-string

Step 4. Closing the file

Code:
{if-non-null stream_variable_name then
    {stream_variable_name.close}
}

Repeat Expressions

until expression (processing repeats until conditional expression is true)

Code:
{until conditional_expression do
    body
}

for expression (specifying a range)

Code:
{for repeat variable:int = initial_value to final_value step step_size value do
    body
}

As well as to, there are also the below, downto, and above keywords. The step_size can be omitted when the desired step_size is 1.

for expression (repeats only the values among the elements of a collection, such as an array)

Code:
{for element_variable:element_type key key_variable[:key type] in (collection) name do
    processing
}

Note that element_variable:Element_type or key key_variable: key_type can be omitted.

Exception Processing

Code:
{try
    Processing in which an exception may occur.
catch exception_variable_name: exception
    Exception Processing
finally
    Processing that must be performed regardless of whether an exception occurs
}

The catch and finally clauses can be omitted. Also, each try can be declared more than once.]]> <![CDATA[Page 6: Structure of a Program that Reads our Score Data]]> https://communities.curl.com/showthread.php?tid=76 Mon, 20 Jun 2011 04:21:42 +0000 https://communities.curl.com/showthread.php?tid=76 Structure of the program that reads our score data



In this example, the data that is read from the file is displayed using a RecordGrid.

1. Specifying the location of the file

Code:
let loc:Url = {url score.txt}

Specify the location of the file.

2. Declaration of a TextInputStreams

Code:
let in:#TextInputStream

To read data from the file, we have to declare TextInputStream.

3. Declaration of character string array used to save read-in data

Code:
let data-array:StringArray = {StringArray}

Declare the character string array to be used for the data read from a file.

4. Declaration of RecordSet used to store data

Code:
let record-set:RecordSet =
    {RecordSet
        {RecordFields
            {RecordField name, domain = String},
            {RecordField age, domain = int},
            {RecordField score, domain = int}
        }
    }

In this sample, the data obtained from a file is converted to a RecordSet, and then later displayed using RecordGrid.

5. Opening a file

Code:
set in = {read-open loc}

Using read-open, we open the specified file as a TextInputStream.

6. Reading the data

Code:
{until in.end-of-stream? do
    {if-non-null line = {in.read-line} then
        {data-array.append {line.to-String}}
    }
}

The data is read, line-by-line, and then added to the character string array.

7. Closing the file

Code:
{if-non-null in then
    {in.close}
}

Regardless of whether the data read from the file is successful or not, the open file must be closed.

8. Data conversion

Code:
{for data:String in data-array do
    let array:StringArray = {data.split split-chars = ,}
    {if array.size == 3 then
        {record-set.append
            {RecordData
                name = array[0], age = {array[1].to-int}, score = {array[2].to-int}
            }
        }
    }
}

We have to convert the data that is stored in a StringArray to a RecordSet. Each line of data in the file corresponds to one record. Also, each field is delimited by a comma (,). So, using the String.split method and a comma (,) as the delimiter, we partition the data and then save it into an array. Using the data in that array, we create RecordData, and then add it to a RecordSet.

9. Displaying the layout

Code:
{RecordGrid
    record-source = record-set,
    width = 10cm,
    height = 3cm
}

We take the RecordSet that we created in (8) and then display it using a RecordGrid.


Working with CSV Data

The Curl language also provides a predefined API for reading and writing CSV (comma separated values) formatted files. Using CsvRecordSet, you can load data directly as a RecordSet for further manipulation and/or display. Please refer to the Curl documentation for more information

]]> Structure of the program that reads our score data



In this example, the data that is read from the file is displayed using a RecordGrid.

1. Specifying the location of the file

Code:
let loc:Url = {url score.txt}

Specify the location of the file.

2. Declaration of a TextInputStreams

Code:
let in:#TextInputStream

To read data from the file, we have to declare TextInputStream.

3. Declaration of character string array used to save read-in data

Code:
let data-array:StringArray = {StringArray}

Declare the character string array to be used for the data read from a file.

4. Declaration of RecordSet used to store data

Code:
let record-set:RecordSet =
    {RecordSet
        {RecordFields
            {RecordField name, domain = String},
            {RecordField age, domain = int},
            {RecordField score, domain = int}
        }
    }

In this sample, the data obtained from a file is converted to a RecordSet, and then later displayed using RecordGrid.

5. Opening a file

Code:
set in = {read-open loc}

Using read-open, we open the specified file as a TextInputStream.

6. Reading the data

Code:
{until in.end-of-stream? do
    {if-non-null line = {in.read-line} then
        {data-array.append {line.to-String}}
    }
}

The data is read, line-by-line, and then added to the character string array.

7. Closing the file

Code:
{if-non-null in then
    {in.close}
}

Regardless of whether the data read from the file is successful or not, the open file must be closed.

8. Data conversion

Code:
{for data:String in data-array do
    let array:StringArray = {data.split split-chars = ,}
    {if array.size == 3 then
        {record-set.append
            {RecordData
                name = array[0], age = {array[1].to-int}, score = {array[2].to-int}
            }
        }
    }
}

We have to convert the data that is stored in a StringArray to a RecordSet. Each line of data in the file corresponds to one record. Also, each field is delimited by a comma (,). So, using the String.split method and a comma (,) as the delimiter, we partition the data and then save it into an array. Using the data in that array, we create RecordData, and then add it to a RecordSet.

9. Displaying the layout

Code:
{RecordGrid
    record-source = record-set,
    width = 10cm,
    height = 3cm
}

We take the RecordSet that we created in (8) and then display it using a RecordGrid.


Working with CSV Data

The Curl language also provides a predefined API for reading and writing CSV (comma separated values) formatted files. Using CsvRecordSet, you can load data directly as a RecordSet for further manipulation and/or display. Please refer to the Curl documentation for more information

]]> <![CDATA[Page 5: Application: Reading Our Score Data]]> https://communities.curl.com/showthread.php?tid=75 Mon, 20 Jun 2011 04:20:03 +0000 https://communities.curl.com/showthread.php?tid=75 Application: Reading Our Score Data

We’ll read the data containing our scores, and then display it.

Create the 'Try 5-3' Project

Close the Try 5-2 project and then, from the IDE 'File' menu, select 'New Project'. In the 'New Project' dialog box, select “Applet Project” (1), input “Try5-3” (2), specify c:\Curl\lesson\Try5\03_score_file in the “Directory” field (3), set the API Version to 6.0 (4), and then click OK (5).



Inputting the Program

Copy the c:\Curl\Try5\03_score_file\score.txt file to the c:\Curl\lesson\Try5\03_score_file directory. Next, we’ll input the program. You can copy the program code below or use c:\Curl\Try5\03_score_file\start.curl and then paste it into the editor in the IDE.



Code:
{value
    let loc:Url = {url score.txt}
    let in:#TextInputStream
    let data-array:StringArray = {StringArray}
    let record-set:RecordSet = {RecordSet
                                   {RecordFields
                                       {RecordField name, domain = String},
                                       {RecordField age, domain = int},
                                       {RecordField score, domain = int}
                                   }
                               }
    
    {try
        set in = {read-open loc}
        {until in.end-of-stream? do
            {if-non-null line = {in.read-line} then
                {data-array.append {line.to-String}}
            }
        }
     catch e:IOException do
        {popup-message Error reading file}
        {output e.message}
     finally
        {if-non-null in then
            {in.close}
        }
    }
    
    {for data:String in data-array do
        let array:StringArray = {data.split split-chars = ,}
        {if array.size == 3 then
            {record-set.append
                {RecordData
                    name = array[0], age = {array[1].to-int}, score = {array[2].to-int}
                }
            }
        }
    }
    
    {RecordGrid
        record-source = record-set,
        width = 10cm,
        height = 3cm
    }
}

Save the File, and then Execute the Program

After inputting the code, save the file, and then execute the program. The following result will appear in your browser.

]]> Application: Reading Our Score Data

We’ll read the data containing our scores, and then display it.

Create the 'Try 5-3' Project

Close the Try 5-2 project and then, from the IDE 'File' menu, select 'New Project'. In the 'New Project' dialog box, select “Applet Project” (1), input “Try5-3” (2), specify c:\Curl\lesson\Try5\03_score_file in the “Directory” field (3), set the API Version to 6.0 (4), and then click OK (5).



Inputting the Program

Copy the c:\Curl\Try5\03_score_file\score.txt file to the c:\Curl\lesson\Try5\03_score_file directory. Next, we’ll input the program. You can copy the program code below or use c:\Curl\Try5\03_score_file\start.curl and then paste it into the editor in the IDE.



Code:
{value
    let loc:Url = {url score.txt}
    let in:#TextInputStream
    let data-array:StringArray = {StringArray}
    let record-set:RecordSet = {RecordSet
                                   {RecordFields
                                       {RecordField name, domain = String},
                                       {RecordField age, domain = int},
                                       {RecordField score, domain = int}
                                   }
                               }
    
    {try
        set in = {read-open loc}
        {until in.end-of-stream? do
            {if-non-null line = {in.read-line} then
                {data-array.append {line.to-String}}
            }
        }
     catch e:IOException do
        {popup-message Error reading file}
        {output e.message}
     finally
        {if-non-null in then
            {in.close}
        }
    }
    
    {for data:String in data-array do
        let array:StringArray = {data.split split-chars = ,}
        {if array.size == 3 then
            {record-set.append
                {RecordData
                    name = array[0], age = {array[1].to-int}, score = {array[2].to-int}
                }
            }
        }
    }
    
    {RecordGrid
        record-source = record-set,
        width = 10cm,
        height = 3cm
    }
}

Save the File, and then Execute the Program

After inputting the code, save the file, and then execute the program. The following result will appear in your browser.

]]> <![CDATA[Page 4: Structure of a Program that Writes Data to a File]]> https://communities.curl.com/showthread.php?tid=74 Mon, 20 Jun 2011 04:18:54 +0000 https://communities.curl.com/showthread.php?tid=74 Structure of the Program that Writes Data to a File



The prcoess for writing data into a file is similar to reading data from a file.

1. Declaring a TextOutputStream

Code:
let out:#TextOutputStream

To write data into a file, we use TextOutputStream. In the same way as in Try 5-1, we declare this variable so it can have a null value.

2. Creating VBox for display

Code:
let v:VBox = {VBox spacing = 3.5pt, margin = 10pt, halign = right}

We declare a VBox, which is used for displaying the layout. We also specify spacing property which defines the spacing between objects, and the margin attribute that defines the amount of white space around the outside edges. The property halign is used to align all child objects to the right side of the VBox.

3. Declaring the character string array used for the titles

Code:
let title-array:StringArray =
    {StringArray
        Name: , Company: , Address: ,
        Phone: , Email:
    }

We declare the above character strings as an array. These will eventually be displayed in the layout.

4. Declaring the input field array

Code:
let field-array:{Array-of TextField} = {{Array-of TextField}}

We create the array for the input text fields. The initial value is an empty array, that is, one that does not contain any elements.

5. Adding the input fields to the layout

Code:
{for i:int = 0 below 5 do
    {field-array.append {TextField width = 5cm}}
    {v.add
        {HBox
            title-array+,
            field-array+
        }
    }
}

This time, we use the for expression to iterate over a specified range. Because we’ve specified below, the processing is not performed when i = 5 and the loop ends at that point. For each iteration of the for expression, we add a new TextField to the array. Finally, in the VBox used for the layout, we add an element from the title-array and one from the field-array.

6. Specifying a location for the file

Code:
if-non-null loc = {choose-file style = save-as} then

In Try 5-1, we specified the URL of a file directly in the program text. In this example, however, we use a procedure called choose-file. choose-file pops up a Save as dialog box. If the user then specifies a file, that file's URL is returned as a return value.

7. Opening a File

Code:
set out = {write-open
              error-if-exists? = true,
              loc
          }

To write data into a file, we use the write-open procedure. With write-open, if the specified file already exists, by default the data in that file will be overwritten.

We can also call write-open in a way that prohibits the overwriting of an existing file. If we specify error-if-exists ?= true and we attempt to write data to an existing file, an exception called ExistingFileException will be thrown.

Note that if we want to append data to a file, we would use append-open instead of write-open.

8. Writing data

Code:
{for tx:TextField in field-array do
    {out.write-one-string tx.value & "\r\n"}
}

Using the write-one-string method, we can write a single character string. We can also use the for expression to obtain, in order, each TextField in an array, and then write the obtained values into a file. \r\n is used to indicate a carriage return and newline respectively.

In the same way as for reading data, there are several different methods for writing data such as write, write-one, and write-one-string. Please consult the Curl documentation for a full listing.

9. Handling an exception

Code:
catch e:ExistingFileException do
  {popup-message That file already exists.}
  {output e.message}
catch e:IOException do
  {popup-message Error writing to file.}
  {output e.message}

Here, we use multiple catch clauses to perform the exception processing.

10. Closing the files

Code:
{if-non-null out then
    {out.close}
}

We have to close the file in exactly the same way as when we read data.


Privileges and choose-file

Curl applets without the necessary privileges cannot freely access local resources. If, however, we use the choose-file procedure to specify the location of a file (like we did in Try 5-2), then even applets without special privileges can access user files. For an explanation of privileges, see Try 0 Page 2 or the Curl documentation.
]]> Structure of the Program that Writes Data to a File



The prcoess for writing data into a file is similar to reading data from a file.

1. Declaring a TextOutputStream

Code:
let out:#TextOutputStream

To write data into a file, we use TextOutputStream. In the same way as in Try 5-1, we declare this variable so it can have a null value.

2. Creating VBox for display

Code:
let v:VBox = {VBox spacing = 3.5pt, margin = 10pt, halign = right}

We declare a VBox, which is used for displaying the layout. We also specify spacing property which defines the spacing between objects, and the margin attribute that defines the amount of white space around the outside edges. The property halign is used to align all child objects to the right side of the VBox.

3. Declaring the character string array used for the titles

Code:
let title-array:StringArray =
    {StringArray
        Name: , Company: , Address: ,
        Phone: , Email:
    }

We declare the above character strings as an array. These will eventually be displayed in the layout.

4. Declaring the input field array

Code:
let field-array:{Array-of TextField} = {{Array-of TextField}}

We create the array for the input text fields. The initial value is an empty array, that is, one that does not contain any elements.

5. Adding the input fields to the layout

Code:
{for i:int = 0 below 5 do
    {field-array.append {TextField width = 5cm}}
    {v.add
        {HBox
            title-array+,
            field-array+
        }
    }
}

This time, we use the for expression to iterate over a specified range. Because we’ve specified below, the processing is not performed when i = 5 and the loop ends at that point. For each iteration of the for expression, we add a new TextField to the array. Finally, in the VBox used for the layout, we add an element from the title-array and one from the field-array.

6. Specifying a location for the file

Code:
if-non-null loc = {choose-file style = save-as} then

In Try 5-1, we specified the URL of a file directly in the program text. In this example, however, we use a procedure called choose-file. choose-file pops up a Save as dialog box. If the user then specifies a file, that file's URL is returned as a return value.

7. Opening a File

Code:
set out = {write-open
              error-if-exists? = true,
              loc
          }

To write data into a file, we use the write-open procedure. With write-open, if the specified file already exists, by default the data in that file will be overwritten.

We can also call write-open in a way that prohibits the overwriting of an existing file. If we specify error-if-exists ?= true and we attempt to write data to an existing file, an exception called ExistingFileException will be thrown.

Note that if we want to append data to a file, we would use append-open instead of write-open.

8. Writing data

Code:
{for tx:TextField in field-array do
    {out.write-one-string tx.value & "\r\n"}
}

Using the write-one-string method, we can write a single character string. We can also use the for expression to obtain, in order, each TextField in an array, and then write the obtained values into a file. \r\n is used to indicate a carriage return and newline respectively.

In the same way as for reading data, there are several different methods for writing data such as write, write-one, and write-one-string. Please consult the Curl documentation for a full listing.

9. Handling an exception

Code:
catch e:ExistingFileException do
  {popup-message That file already exists.}
  {output e.message}
catch e:IOException do
  {popup-message Error writing to file.}
  {output e.message}

Here, we use multiple catch clauses to perform the exception processing.

10. Closing the files

Code:
{if-non-null out then
    {out.close}
}

We have to close the file in exactly the same way as when we read data.


Privileges and choose-file

Curl applets without the necessary privileges cannot freely access local resources. If, however, we use the choose-file procedure to specify the location of a file (like we did in Try 5-2), then even applets without special privileges can access user files. For an explanation of privileges, see Try 0 Page 2 or the Curl documentation.
]]> <![CDATA[Page 3: Basics 2: Writing a Control Value into a File]]> https://communities.curl.com/showthread.php?tid=73 Mon, 20 Jun 2011 04:16:35 +0000 https://communities.curl.com/showthread.php?tid=73 Basics 2: Writing a Control Value into a File

Create the 'Try 5-2' Project

Close the Try 5-1 project and then, from the IDE 'File' menu, select 'New Project'. In the 'New Project' dialog box, select “Applet Project” (1), input “Try5-2” (2), specify c:\Curl\lesson\Try5\02_write_file in the “Directory” field (3), set the API Version to 6.0 (4), and then click OK (5).


Inputting the Program

Next, we’ll input the program. You can copy the program code below or use c:\Curl\Try5\02_write_file\start.curl and then paste it into the editor in the IDE.

Code:
{value
    let out:#TextOutputStream
    let v:VBox = {VBox spacing = 3.5pt, margin = 10pt, halign = right}    
    let title-array:StringArray = {StringArray
                                      Name: , Company: , Address: ,
                                      Phone: , Email:
                                  }
    let field-array:{Array-of TextField} = {{Array-of TextField}}
    
    {for i:int = 0 below 5 do
        {field-array.append {TextField width = 5cm}}
        {v.add
            {HBox
                title-array+,
                field-array+
            }
        }
    }
    
    {v.add
        {CommandButton
            label = Save,
            {on Action do
                {if-non-null loc = {choose-file style = save-as} then
                    {try
                        set out = {write-open
                                      error-if-exists? = true,
                                      loc
                                  }
                        {for tx:TextField in field-array do
                            {out.write-one-string tx.value & "\r\n}
                        }
                     catch e:ExistingFileException do
                        {popup-message That file already exists.}
                        {output e.message}
                     catch e:IOException do
                        {popup-message Error writing to file."}
                        {output e.message}
                     finally
                        {if-non-null out then
                            {out.close}
                        }
                    }
                 else
                }
            }
        }
    }
    v
}

Save the File, and then Execute the Program

After inputting the code, save the file, and then execute the program. The execution results are displayed by the browser ((1)). Input values into a text fields, and then click the \[Save\] button ((2)). The “Save as” dialog box is displayed. This lets us create a new text file and then save the data to a convenient location. If we check the contents of the text file, then we should find that it contains the data that we entered.
]]> Basics 2: Writing a Control Value into a File

Create the 'Try 5-2' Project

Close the Try 5-1 project and then, from the IDE 'File' menu, select 'New Project'. In the 'New Project' dialog box, select “Applet Project” (1), input “Try5-2” (2), specify c:\Curl\lesson\Try5\02_write_file in the “Directory” field (3), set the API Version to 6.0 (4), and then click OK (5).


Inputting the Program

Next, we’ll input the program. You can copy the program code below or use c:\Curl\Try5\02_write_file\start.curl and then paste it into the editor in the IDE.

Code:
{value
    let out:#TextOutputStream
    let v:VBox = {VBox spacing = 3.5pt, margin = 10pt, halign = right}    
    let title-array:StringArray = {StringArray
                                      Name: , Company: , Address: ,
                                      Phone: , Email:
                                  }
    let field-array:{Array-of TextField} = {{Array-of TextField}}
    
    {for i:int = 0 below 5 do
        {field-array.append {TextField width = 5cm}}
        {v.add
            {HBox
                title-array+,
                field-array+
            }
        }
    }
    
    {v.add
        {CommandButton
            label = Save,
            {on Action do
                {if-non-null loc = {choose-file style = save-as} then
                    {try
                        set out = {write-open
                                      error-if-exists? = true,
                                      loc
                                  }
                        {for tx:TextField in field-array do
                            {out.write-one-string tx.value & "\r\n}
                        }
                     catch e:ExistingFileException do
                        {popup-message That file already exists.}
                        {output e.message}
                     catch e:IOException do
                        {popup-message Error writing to file."}
                        {output e.message}
                     finally
                        {if-non-null out then
                            {out.close}
                        }
                    }
                 else
                }
            }
        }
    }
    v
}

Save the File, and then Execute the Program

After inputting the code, save the file, and then execute the program. The execution results are displayed by the browser ((1)). Input values into a text fields, and then click the \[Save\] button ((2)). The “Save as” dialog box is displayed. This lets us create a new text file and then save the data to a convenient location. If we check the contents of the text file, then we should find that it contains the data that we entered.
]]> <![CDATA[Page 2: Structure of a Program that Reads Data from a File]]> https://communities.curl.com/showthread.php?tid=72 Mon, 20 Jun 2011 04:13:53 +0000 https://communities.curl.com/showthread.php?tid=72 Structure of the Program that Reads Data from a File

First, let’s consider how we can read the data that is written into a file. There are actually four steps involved in reading such data. These are as follows:
  • Step 1: Specifying the location of the file
  • Step 2: Opening the file
  • Step 3: Reading the data
  • Step 4: Closing the file

Let’s start by taking a look at the program’s source code.



1. Specifying the location of the file (Step 1)

Code:
let loc:Url = {url data.txt}

In the first step we need to specify the location of the file we will be reading. The location of the file is specified with a variable called a Url. In the url procedure, we set a character string value that specifies the path to the file.

2. Declaring TextInputStream

Code:
let input: #TextInputStream

To read a text file, we use TextInputStream. In this example, an initial value is not set for the variable declaration. In this case, we preceed TextInputStream with a # so that the default value (null) will be legal.

3. Declaring the character string array that is used to store the read datas

Code:
let data-array:StringArray = {StringArray}

Here, data is read from the file line-by-line and then saved into a StringArray. StringArray is an abbreviation for {Array-of String}.

4. Creating the variables that are used for display

Code:
let list:DropdownList = {DropdownList width = 5cm}

We declare the list variable as a DropdownList that is used to display the read-in data.

5. Exception processing

Code:
{try
    ... (code here) ...
    
catch e:IOException do
    {popup-message Error reading file}
    {output e.message}
    
finally
    ... (code here) ...
}

If the file cannot be opened or read, the Curl RTE detects that the operatio cannot be completed normally. This is known as an exception. If an exception occurs, this program performs exception processing to prevent an error with the applet.

In our example, when the file at the specified URL is opened, an exception may occur when data is read from the file.

To handle an exception, we use the try expression. That location at which an exception may occur is enclosed in the try expression. Also, we define a catch clause that handles exceptions that may occur.

For every try expression, we can define multiple catch clauses. Each catch clause is used to define a specific exception to be handled. In our example, we specify an IOException because we are dealing with input/output operations. It is also possible to catch all exceptions by specifying Exception for the type of the exception processed by each catch phrase.

At the end, we use the finally clause to describe processing that must be performed regardless of whether an exception has occurred.


Exception Processing

Code:
{try
    body
    [catch-clauses]
    [finally-clause]
}

where
  • body is one or more Curl language expressions (this is the code that throws the exception).
  • catch-clauses is zero or more optional catch clauses.
  • finally-clause is an optional finally clause.


6. Opening a file (Step 2)

Code:
set input = {read-open loc}

TextInputStream is opened from the file URL; this is the second step. Using the read-open procedure, we specify the URL as the argument and the file is opened as a TextInputStream.

7. Opening a file (Step 3)

Code:
{until input.end-of-stream? do
    {if-non-null line = {input.read-line} then
        {data-array.append {line.to-String}}
    }
}

After the file is opened as a TextInputStream, the data is read using the until expression. In this case, the code block is processed repeatedly until the specified boolean expression becomes true.

There are three types looping expressions in Curl: until, while, and for. Let's look at the until and while expressions now (we'll cover the for expression later). These two expressions have a body that is repeatedly executed until a specified expression becomes either true or false.


until expression

Code:
{until conditional_expression do
    
}

until processing is repeated until the condition is true.


while expression

Code:
{while conditional_expression do
    
}

while processing is repeated until the condition is false.


Now, let’s take a look at our example.

Code:
{until input.end-of-stream? do
    
}

In the example, the input.end-of-stream? expression indicates the condition. When the TextInputStream reaches the end of the stream, the expression returns a value of true, so, the until expression is repeatedly processed until it reaches the end of the stream.


Streams

Streams are sequences of data that your applets can either read from or write to. They create a generic interface for exchanging data with resources.


The next expression in our example is if-non-null. This expression is very similar to the if, but the if-non-null expression branches based on whether the value is of the expression is null or not (rather than true or false). Therefore, when the value of the expression is non-null, the the specified code block is executed.



if-non-null

Code:
{if-non-null [var-name[:type] = ] expr
then if-body
    [elseif cond then elseif-body]
    [else else-body]
}
  • When the expression is not null, processing is performed
  • The elseif and else phrases can be omitted.


Let’s take a look at the example.

Code:
{if-non-null line = {input.read-line} then
    {data-array.append {line.to-String}
    }
}

The input.read-line method lets us read data from the TextInputStream line by line. In our example, whenever the value is non-null, one line of data has been read. The text of each line read will be appended to an array. In addition to read-line, there are several methods for reading data.

Finally, let’s take a look at the processing following the if-non-null expression. data-array is a String array, as described above. Using the append method, we can add an element to an array. The following table describes other methods that can be used to manipulate array contents.



The input.read-line method returns the data that has been read from a file. This value is returned as a StringBuf. Since elements of this array are of String type, we use the to-String method to convert from StringBuf to String. The value is then added to the array.

In summary, the processing performed involves reading all the stream data line-by-line and provided that data is non-null, converting the data to a String and adding it to the array.

8. Closing the file (Step 4)

Code:
{if-non-null input then
    {input.close}
}

The file is closed after the data is read from the file. A close must always be performed, regardless of whether an exception has occurred, so it is performed in the finally clause. In our example, we use if-non-null to check whether the file was ever opened. If the file is open, the close method is used to close the file.

9. Adding elements to the drop-down list

Code:
{for s:String in data-array do
    {list.append s}
}

Since the data that is read from a file is stored in the array named data-array, we can access each element as input for our dropdown list. The data is taken, in order, and then added to a DropdownList control named list. The body of the for expression is executed repeatedly, each time adding another element to the DropdownList.

Curl supports two variations of the for expression. The first is used to specify a range and executes the body for each value in the range, while the second executes the body for each value in a collection of elements, such as an array.


What is a Collection?

A “collection” is a group of elements, all of which are of the same data type. Arrays and hash tables are both typical examples of collections.


for expression, executed repeatedly within a given range

Code:
{for repeat variable:int = initial_value to final_value step step_size do
    body
}


If we omit step step_size, the variable value is increased (or decreased), by 1 each.

Instead of to, we can also specify below, downto, or above.
  • to … Variable value is increased in increments of the step_size. Processing is repeated while the variable value is less than or equal to the final value.
  • below … Variable value is increased in increments of the step_size. Processing is repeated while the variable value is less than the final value.
  • downto … Variable value is decreased in increments of the step_size. Processing is repeated while the variable value is greater than or equal to the final value.
  • above … Variable value is decreased in increments of the step_size. Processing is repeated while the variable value is greater than the final value.

Let’s execute the following two pieces of source code and see how the results differ. When we use to, the results should be 0 2 4 6 8. When we use below, it should return 0 2 4 6.
  • When we use to

Code:
{value
    let message:HBox = {HBox}
    {for x:int = 0 to 8 step 2 do
        {message.add x}
    }
    message
}


  • When we use below

Code:
{value
    let message:HBox = {HBox}
    {for x:int = 0 below 8 step 2 do
        {message.add x}
    }
    message
}



The for expression that takes its values from the elements of a collection, will be as follows:


for expression

Code:
{for element _variable[:element_type] key key_variable[:key_type] in collection_name do
    processing
}


In our example, we use the for expression which repeats only the values among the elements of an array. The data is extracted from the element values in the array, and then added as items to be shown in the dropdown list.

10. Adding an event handler

Code:
{list.add-event-handler
    {on ValueChanged at lb:DropdownList do
        {popup-message lb.value & [color=red]was selected}
    }
}

Curl supports a method for adding an event handler, as mentioned in Try 2. We can use this method to specify that, when a value is selected from the dropdown list, it is displayed in a pop-up window.

11. Specifying the layout

Code:
{VBox
    [color=red]Select a US state[/color],
    list
}

We specify the screen display layout at the end of value. Character strings and the dropdown list are arranged vertically.

.png   5-1.PNG (Size: 12.23 KB / Downloads: 1256) ]]> Structure of the Program that Reads Data from a File

First, let’s consider how we can read the data that is written into a file. There are actually four steps involved in reading such data. These are as follows:
  • Step 1: Specifying the location of the file
  • Step 2: Opening the file
  • Step 3: Reading the data
  • Step 4: Closing the file

Let’s start by taking a look at the program’s source code.



1. Specifying the location of the file (Step 1)

Code:
let loc:Url = {url data.txt}

In the first step we need to specify the location of the file we will be reading. The location of the file is specified with a variable called a Url. In the url procedure, we set a character string value that specifies the path to the file.

2. Declaring TextInputStream

Code:
let input: #TextInputStream

To read a text file, we use TextInputStream. In this example, an initial value is not set for the variable declaration. In this case, we preceed TextInputStream with a # so that the default value (null) will be legal.

3. Declaring the character string array that is used to store the read datas

Code:
let data-array:StringArray = {StringArray}

Here, data is read from the file line-by-line and then saved into a StringArray. StringArray is an abbreviation for {Array-of String}.

4. Creating the variables that are used for display

Code:
let list:DropdownList = {DropdownList width = 5cm}

We declare the list variable as a DropdownList that is used to display the read-in data.

5. Exception processing

Code:
{try
    ... (code here) ...
    
catch e:IOException do
    {popup-message Error reading file}
    {output e.message}
    
finally
    ... (code here) ...
}

If the file cannot be opened or read, the Curl RTE detects that the operatio cannot be completed normally. This is known as an exception. If an exception occurs, this program performs exception processing to prevent an error with the applet.

In our example, when the file at the specified URL is opened, an exception may occur when data is read from the file.

To handle an exception, we use the try expression. That location at which an exception may occur is enclosed in the try expression. Also, we define a catch clause that handles exceptions that may occur.

For every try expression, we can define multiple catch clauses. Each catch clause is used to define a specific exception to be handled. In our example, we specify an IOException because we are dealing with input/output operations. It is also possible to catch all exceptions by specifying Exception for the type of the exception processed by each catch phrase.

At the end, we use the finally clause to describe processing that must be performed regardless of whether an exception has occurred.


Exception Processing

Code:
{try
    body
    [catch-clauses]
    [finally-clause]
}

where
  • body is one or more Curl language expressions (this is the code that throws the exception).
  • catch-clauses is zero or more optional catch clauses.
  • finally-clause is an optional finally clause.


6. Opening a file (Step 2)

Code:
set input = {read-open loc}

TextInputStream is opened from the file URL; this is the second step. Using the read-open procedure, we specify the URL as the argument and the file is opened as a TextInputStream.

7. Opening a file (Step 3)

Code:
{until input.end-of-stream? do
    {if-non-null line = {input.read-line} then
        {data-array.append {line.to-String}}
    }
}

After the file is opened as a TextInputStream, the data is read using the until expression. In this case, the code block is processed repeatedly until the specified boolean expression becomes true.

There are three types looping expressions in Curl: until, while, and for. Let's look at the until and while expressions now (we'll cover the for expression later). These two expressions have a body that is repeatedly executed until a specified expression becomes either true or false.


until expression

Code:
{until conditional_expression do
    
}

until processing is repeated until the condition is true.


while expression

Code:
{while conditional_expression do
    
}

while processing is repeated until the condition is false.


Now, let’s take a look at our example.

Code:
{until input.end-of-stream? do
    
}

In the example, the input.end-of-stream? expression indicates the condition. When the TextInputStream reaches the end of the stream, the expression returns a value of true, so, the until expression is repeatedly processed until it reaches the end of the stream.


Streams

Streams are sequences of data that your applets can either read from or write to. They create a generic interface for exchanging data with resources.


The next expression in our example is if-non-null. This expression is very similar to the if, but the if-non-null expression branches based on whether the value is of the expression is null or not (rather than true or false). Therefore, when the value of the expression is non-null, the the specified code block is executed.



if-non-null

Code:
{if-non-null [var-name[:type] = ] expr
then if-body
    [elseif cond then elseif-body]
    [else else-body]
}
  • When the expression is not null, processing is performed
  • The elseif and else phrases can be omitted.


Let’s take a look at the example.

Code:
{if-non-null line = {input.read-line} then
    {data-array.append {line.to-String}
    }
}

The input.read-line method lets us read data from the TextInputStream line by line. In our example, whenever the value is non-null, one line of data has been read. The text of each line read will be appended to an array. In addition to read-line, there are several methods for reading data.

Finally, let’s take a look at the processing following the if-non-null expression. data-array is a String array, as described above. Using the append method, we can add an element to an array. The following table describes other methods that can be used to manipulate array contents.



The input.read-line method returns the data that has been read from a file. This value is returned as a StringBuf. Since elements of this array are of String type, we use the to-String method to convert from StringBuf to String. The value is then added to the array.

In summary, the processing performed involves reading all the stream data line-by-line and provided that data is non-null, converting the data to a String and adding it to the array.

8. Closing the file (Step 4)

Code:
{if-non-null input then
    {input.close}
}

The file is closed after the data is read from the file. A close must always be performed, regardless of whether an exception has occurred, so it is performed in the finally clause. In our example, we use if-non-null to check whether the file was ever opened. If the file is open, the close method is used to close the file.

9. Adding elements to the drop-down list

Code:
{for s:String in data-array do
    {list.append s}
}

Since the data that is read from a file is stored in the array named data-array, we can access each element as input for our dropdown list. The data is taken, in order, and then added to a DropdownList control named list. The body of the for expression is executed repeatedly, each time adding another element to the DropdownList.

Curl supports two variations of the for expression. The first is used to specify a range and executes the body for each value in the range, while the second executes the body for each value in a collection of elements, such as an array.


What is a Collection?

A “collection” is a group of elements, all of which are of the same data type. Arrays and hash tables are both typical examples of collections.


for expression, executed repeatedly within a given range

Code:
{for repeat variable:int = initial_value to final_value step step_size do
    body
}


If we omit step step_size, the variable value is increased (or decreased), by 1 each.

Instead of to, we can also specify below, downto, or above.
  • to … Variable value is increased in increments of the step_size. Processing is repeated while the variable value is less than or equal to the final value.
  • below … Variable value is increased in increments of the step_size. Processing is repeated while the variable value is less than the final value.
  • downto … Variable value is decreased in increments of the step_size. Processing is repeated while the variable value is greater than or equal to the final value.
  • above … Variable value is decreased in increments of the step_size. Processing is repeated while the variable value is greater than the final value.

Let’s execute the following two pieces of source code and see how the results differ. When we use to, the results should be 0 2 4 6 8. When we use below, it should return 0 2 4 6.
  • When we use to

Code:
{value
    let message:HBox = {HBox}
    {for x:int = 0 to 8 step 2 do
        {message.add x}
    }
    message
}


  • When we use below

Code:
{value
    let message:HBox = {HBox}
    {for x:int = 0 below 8 step 2 do
        {message.add x}
    }
    message
}



The for expression that takes its values from the elements of a collection, will be as follows:


for expression

Code:
{for element _variable[:element_type] key key_variable[:key_type] in collection_name do
    processing
}


In our example, we use the for expression which repeats only the values among the elements of an array. The data is extracted from the element values in the array, and then added as items to be shown in the dropdown list.

10. Adding an event handler

Code:
{list.add-event-handler
    {on ValueChanged at lb:DropdownList do
        {popup-message lb.value & [color=red]was selected}
    }
}

Curl supports a method for adding an event handler, as mentioned in Try 2. We can use this method to specify that, when a value is selected from the dropdown list, it is displayed in a pop-up window.

11. Specifying the layout

Code:
{VBox
    [color=red]Select a US state[/color],
    list
}

We specify the screen display layout at the end of value. Character strings and the dropdown list are arranged vertically.

.png   5-1.PNG (Size: 12.23 KB / Downloads: 1256) ]]> <![CDATA[Page 1: Reading Our Score Data]]> https://communities.curl.com/showthread.php?tid=71 Mon, 20 Jun 2011 04:12:52 +0000 https://communities.curl.com/showthread.php?tid=71 Try 5: Reading Our Score Data

Please download the Try5.zip file by selecting the following link: Try5.zip.

Unzip the contents to the C:\Curl directory. This is the working directory for all the examples and exercises contained within this tutorial. Note: If C:\Curl has not already been created, you can create it now.

Basics: Reading Data from a File, Line by Line

Create the 'Try 5-1' Project

Close the Try 4 project and then, from the IDE 'File' menu, select 'New Project'. In the 'New Project' dialog box, select “Applet Project” (1), input “Try5-1” (2), specify c:\Curl\lesson\Try5\01_read_file in the “Directory” field (3), set the API Version to 6.0 (4), and then click OK (5).


Inputting the Program

Copy the c:\Curl\Try5\01_read_file\data.txt file to c:\Curl\lesson\Try5\01_read_file. Next, we’ll input the program. You can copy the program code below or use c:\Curl\Try5\01_read_file\start.curl and then paste it into the editor in the IDE.

Code:
{value
let loc:Url = {url data.txt}
let input:#TextInputStream
let data-array:StringArray = {StringArray}
let list:DropdownList = {DropdownList width = 5cm}

{try
     set input = {read-open loc}
     {until input.end-of-stream? do
         {if-non-null line = {input.read-line} then
             {data-array.append {line.to-String}}
         }
     }
    
  catch e:IOException do
     {popup-message An error reading the file has occurred.}
     {output e.message}
        
  finally
     {if-non-null input then
         {input.close}
     }
}

{for s:String in data-array do
     {list.append s}
}

{list.add-event-handler
     {on ValueChanged at lb:DropdownList do
         {popup-message lb.value &  was selected}
      
     }
}

{VBox
     Please select a state,
     list
}
}

Save the File, and then Execute the Program

After inputting the code, save the file, and then execute the program. The following result will appear in your browser.
]]> Try 5: Reading Our Score Data

Please download the Try5.zip file by selecting the following link: Try5.zip.

Unzip the contents to the C:\Curl directory. This is the working directory for all the examples and exercises contained within this tutorial. Note: If C:\Curl has not already been created, you can create it now.

Basics: Reading Data from a File, Line by Line

Create the 'Try 5-1' Project

Close the Try 4 project and then, from the IDE 'File' menu, select 'New Project'. In the 'New Project' dialog box, select “Applet Project” (1), input “Try5-1” (2), specify c:\Curl\lesson\Try5\01_read_file in the “Directory” field (3), set the API Version to 6.0 (4), and then click OK (5).


Inputting the Program

Copy the c:\Curl\Try5\01_read_file\data.txt file to c:\Curl\lesson\Try5\01_read_file. Next, we’ll input the program. You can copy the program code below or use c:\Curl\Try5\01_read_file\start.curl and then paste it into the editor in the IDE.

Code:
{value
let loc:Url = {url data.txt}
let input:#TextInputStream
let data-array:StringArray = {StringArray}
let list:DropdownList = {DropdownList width = 5cm}

{try
     set input = {read-open loc}
     {until input.end-of-stream? do
         {if-non-null line = {input.read-line} then
             {data-array.append {line.to-String}}
         }
     }
    
  catch e:IOException do
     {popup-message An error reading the file has occurred.}
     {output e.message}
        
  finally
     {if-non-null input then
         {input.close}
     }
}

{for s:String in data-array do
     {list.append s}
}

{list.add-event-handler
     {on ValueChanged at lb:DropdownList do
         {popup-message lb.value &  was selected}
      
     }
}

{VBox
     Please select a state,
     list
}
}

Save the File, and then Execute the Program

After inputting the code, save the file, and then execute the program. The following result will appear in your browser.
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