XTextWidth(3) Library Functions Manual XTextWidth(3)

XTextWidth, XTextWidth16 - compute text width

int XTextWidth(XFontStruct *font_struct, _Xconst char *string, int count);

int XTextWidth16(XFontStruct *font_struct, _Xconst XChar2b *string, int count);

count
Specifies the character count in the specified string.
font_struct
Specifies the font used for the width computation.
string
Specifies the character string.

The XTextWidth and XTextWidth16 functions return the width of the specified 8-bit or 2-byte character strings.

XLoadFont(3), XTextExtents(3)
Xlib - C Language X Interface
X Version 11 XLIB FUNCTIONS