# TextSrc Object

    Application Header file <X11/Xaw/TextSrc.h>
    Class Header file       <X11/Xaw/TextSrcP.h>
    Class                   textSrcObjectClass
    Class Name              TextSrc
    Superclass              Object

The TextSrc object is the root object for all text sources. Any new text source objects should be subclasses of the TextSrc Object. The TextSrc Class contains all methods the Text widget expects a text source to export.

Since all text sources will have some resources in common the TextSrc defines a few new resources.

## Resources

When creating an TextSrc object instance, the following resources are retrieved from the argument list or from the resource database:

Name | Class | Type | Notes | Default Value
--- | --- | --- | --- | ---
destroyCallback | Callback | XtCallbackList |  | NULL
editType | EditType | EditMode |  | NULL

## Subclassing the TextSrc

The only purpose of the TextSrc Object is to be subclassed. It contains the minimum set of class methods that all text sources must have. All class methods of the TextSrc must be defined, as the Text widget uses them all. While all may be inherited, the direct descendant of TextSrc `must` specify some of them as TextSrc does not contain enough information to be a valid text source by itself. Do not try to use the TextSrc as a valid source for the Text widget; it is not intended to be used as a source by itself and bad things will probably happen.

Function | Inherit with | Public Interface | must specify
--- | --- | --- | ---
Read | XtInheritRead | XawTextSourceRead | yes
Replace | XtInheritReplace | XawTextSourceReplace | no
Scan | XtInheritScan | XawTextSourceScan | yes
Search | XtInheritSearch | XawTextSourceSearch | no
SetSelection | XtInheritSetSelection | XawTextSourceSetSelection | no
ConvertSelection | XtInheritConvertSelection | XawTextSourceConvertSelection | no

### Reading Text.

To read the text in a text source use the `Read` function:

      XawTextPosition Read
      Widget w
      XawTextPosition pos
      XawTextBlock *text_return
      int length

w

  Specifies the TextSrc object.

pos

  Specifies the position of the first character to be read from the text buffer.

text

  Returns the text read from the source.

length

  Specifies the maximum number of characters the TextSrc should return to the application in text_return.

This function returns the text position immediately after the characters read from the text buffer. The function is not required to read length characters if that many characters are in the file, it may break at any point that is convenient to the internal structure of the source. It may take several calls to `Read` before the desired portion of the text buffer is fully retrieved.

### Replacing Text.

To replace or edit the text in a text buffer use the `Replace` function:

      XawTextPosition Replace
      Widget w
      XawTextPositionstart, end
      XawTextBlock *text

w

  Specifies the TextSrc object.

start

  Specifies the position of the first character to be removed from the text buffer. This is also the location to begin inserting the new text.

end

  Specifies the position immediately after the last character to be removed from the text buffer.

text

  Specifies the text to be added to the text source.

This function can return any of the following values:

`XawEditDone`

  The text replacement was successful.

`XawPositionError`

  The edit mode is `XawtextAppend` and `start` is not the last character of the source.

`XawEditError`

  Either the Source was read-only or the range to be deleted is larger than the length of the Source.

The `Replace` arguments `start` and `end` represent the text source character positions for the existing text that is to be replaced by the text in the text block. The characters from start up to but not including end are deleted, and the buffer specified by the text block is inserted in their place. If start and end are equal, no text is deleted and the new text is inserted after start.

### Scanning the TextSrc

To search the text source for one of the predefined boundary types use the `Scan` function:

      XawTextPosition Scan
      Widget w
      XawTextPosition position
      XawTextScanType type
      XawTextScanDirection dir
      int count
      Boolean include

w

  Specifies the TextSrc object.

position

  Specifies the position to begin scanning the source.

type

  Specifies the type of boundary to scan for, may be one of: `XawstPosition`, `XawstWhiteSpace`, `XawstEOL`, `XawstParagraph`, `XawstAll`. The exact meaning of these boundaries is left up to the individual text source.

dir

  Specifies the direction to scan, may be either `XawsdLeft` to search backward, or `XawsdRight` to search forward.

count

  Specifies the number of boundaries to scan for.

include

  Specifies whether the boundary itself should be included in the scan.

The `Scan` function returns the position in the text source of the desired boundary. It is expected to return a valid address for all calls made to it, thus if a particular request is made that would take the text widget beyond the end of the source it must return the position of that end.

### Searching through a TextSrc

To search for a particular string use the `Search` function.

      XawTextPosition Search
      Widget w
      XawTextPosition position
      XawTextScanDirection dir
      XawTextBlock *text

w

  Specifies the TextSrc object.

position

  Specifies the position to begin the search.

dir

  Specifies the direction to search, may be either `XawsdLeft` to search backward, or `XawsdRight` to search forward.

text

  Specifies a text block containing the text to search for.

This function will search through the text buffer attempting to find a match for the string in the text block. If a match is found in the direction specified, then the character location of the first character in the string is returned. If no text was found then `XawTextSearchError` is returned.

### Text Selections

While many selection types are handled by the Text widget, text sources may have selection types unknown to the Text widget. When a selection conversion is requested by the X server the Text widget will first call the `ConvertSelection` function, to attempt the selection conversion.

      Boolean ConvertSelections
      Widget w
      Atom*selection,*target, *type
      caddr_t *value_return
      unsignedlong *length_return
      int *format_return

w

  Specifies the TextSrc object.

selection

  Specifies the type of selection that was requested (e.g. `PRIMARY`).

target

  Specifies the type of the selection that has been requested, which indicates the desired information about the selection (e.g. Filename, Text, Window).

type

  Specifies a pointer to the atom into which the property type of the converted value of the selection is to be stored. For instance, either file name or text might have property type `XA_STRING`.

value_return

  Returns a pointer into which a pointer to the converted value of the selection is to be stored. The selection owner is responsible for allocating this storage. The memory is considered owned by the toolkit, and is freed by XtFree when the Intrinsics selection mechanism is done with it.

length_return

  Returns a pointer into which the number of elements in value is to be stored. The size of each element is determined by format.

format_return

  Returns a pointer into which the size in bits of the data elements of the selection value is to be stored.

If this function returns `True` then the Text widget will assume that the source has taken care of converting the selection, Otherwise the Text widget will attempt to convert the selection itself.

If the source needs to know when the text selection is modified it should define a `SetSelection` procedure:

      void SetSelection
      Widget w
      XawTextPositionstart, end
      Atom selection

w

  Specifies the TextSrc object.

start

  Specifies the character position of the beginning of the new text selection.

end

  Specifies the character position of the end of the new text selection.

selection

  Specifies the type of selection that was requested (e.g. `PRIMARY`).