ISO/IEC TR 24731-1:2007 provides alternative functions for the C Library (as defined in ISO/IEC 9899:1999) that promote safer, more secure programming. The functions verify that output buffers are large enough for the intended result, and return a failure indicator if they are not. Optionally, failing functions call a "runtime-constraint handler" to report the error. Data is never written past the end of an array. All string results are null terminated. In addition, the functions in ISO/IEC TR 24731-1:2007 are re-entrant: they never return pointers to static objects owned by the function.

ISO/IEC TR 24731-1:2007 also contains functions that address insecurities with the C input-output facilities.