XmTextPosition — Data type for a character position within a text string "XmTextPosition" "data types"

XmTextPosition is an integer data type that holds a character's position within a text  string  for  Text
       and TextField.

       An  XmTextPosition  value conceptually points to the gap between two characters.  For example, consider a
       text string consisting of N characters.  A value of 0 refers to the position  immediately  prior  to  the
       first  character.   A  value  of  1 refers to the position in between the first and second characters.  A
       value of N refers to the position immediately following the last character. Therefore, the text string of
       N characters actually contains N+1 positions.

XmTextPosition  —  Data  type for a character position within a text string "XmTextPosition" "data types"
       "XmTextPosition"

XmText(3).

                                                                                               XmTextPosition(3)

       #include <Xm/Xm.h>