XmbTextEscapement, XwcTextEscapement, Xutf8TextEscapement - obtain the
  escapement of text
int XmbTextEscapement(XFontSet font_set, _Xconst char
    *string, int num_bytes);
int XwcTextEscapement(XFontSet font_set, _Xconst wchar_t
    *string, int num_wchars);
int Xutf8TextEscapement(XFontSet font_set, _Xconst char
    *string, int num_bytes);
  - font_set
- Specifies the font set.
- num_bytes
- Specifies the number of bytes in the string argument.
- num_wchars
- Specifies the number of characters in the string argument.
- string
- Specifies the character string.
The XmbTextEscapement, XwcTextEscapement and
  Xutf8TextEscapement functions return the escapement in pixels of the
  specified string as a value, using the fonts loaded for the specified font
  set. The escapement is the distance in pixels in the primary draw direction
  from the drawing origin to the origin of the next character to be drawn,
  assuming that the rendering of the next character is not dependent on the
  supplied string.Regardless of the character rendering order, the escapement is
    always positive.
The function Xutf8TextEscapement is an extension introduced
    by The XFree86 Project, Inc., in their 4.0.2 release. Its presence is
    indicated by the macro X_HAVE_UTF8_STRING.
XmbTextExtents(3), XmbTextPerCharExtents(3) Xlib - C Language X Interface