XmTextFieldGetSubstringWcs — A TextField function
    that retrieves a portion of a wide character internal text buffer
#include <Xm/TextF.h>
int XmTextFieldGetSubstringWcs(
Widget widget,
XmTextPosition start,
int num_chars,
int buffer_size,
wchar_t *buffer);
XmTextFieldGetSubstringWcs retrieves a copy of a portion of
    the internal text buffer of a TextField widget that is stored in a wide
    character format. The function copies a specified number of characters from
    a given start position in the internal text buffer into a buffer provided by
    the application. A NULL terminator is placed at the end of the copied
  data.
  - widget
- Specifies the TextField widget ID.
- start
- Specifies the beginning character position from which the data will be
      retrieved. This is an integer number of characters from the beginning of
      the text buffer. The first character position is 0 (zero).
- num_chars
- Specifies the number of wchar_t characters to be copied into the
      provided buffer.
- buffer_size
- Specifies the size of the supplied buffer as a number of wchar_t
      storage locations. The minimum size is num_chars + 1.
- buffer
- Specifies the wide character buffer into which the internal text buffer
      will be copied.
For a complete definition of TextField and its associated
    resources, see XmTextField(3).
  - XmCOPY_SUCCEEDED
- The function was successful.
- XmCOPY_FAILED
- The function failed because it was unable to copy the specified number of
      characters into the buffer provided. The buffer size may be insufficient.
      The contents of buffer are undefined.
- XmCOPY_TRUNCATED
- The requested number of characters extended beyond the internal buffer.
      The function copied characters to the end of the buffer and terminated the
      string with a NULL terminator; fewer than num_chars characters were
      copied.
XmTextField(3) and XmTextFieldGetSubstring(3).