ISO/IEC 24747:2009 defines extensions to the C Standard Library that is defined in the International Standard for the C programming language (ISO/IEC 9899). Unless otherwise specified, the whole of the C Standard Library is included in ISO/IEC 24747:2009 by reference.

ISO/IEC 24747:2009 defines library extensions to the C Standard Library to support Mathematical Special functions to be added to <math.h> and <tgmath.h>.