FcStrCopyFilename man page
FcStrCopyFilename — create a complete path from a filename
#include <fontconfig/fontconfig.h> FcChar8 * FcStrCopyFilename (const FcChar8 *s);
FcStrCopyFilename constructs an absolute pathname from s. It converts any leading '~' characters in to the value of the HOME environment variable, and any relative paths are converted to absolute paths using the current working directory. Sequences of '/' characters are converted to a single '/', and names containing the current directory '.' or parent directory '..' are correctly reconstructed. Returns NULL if '~' is the leading character and HOME is unset or disabled (see FcConfigEnableHome).