My apologies to testdirector. The standard says modification of string literal is undefined. Remember that 'undefined' does not equal to 'not allowed'. GNU C does not allow it. Others might and IMHO those that do are stupid. This is what I found: The standard says [6.1.4], "If the program attempts to modify [a string literal], the behavior is undefined." and 3.16 undefined behavior: Behavior, upon use of a nonportable or erroneous program construct, or erroneous data, or of indeterminately valued objects, for which this International Standard imposes no requirements. Permissible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic method), to terminating a translation or execution (with the issuance of a diagnostic message). and 4 Compliance A strictly conforming program shall ... not produce output dependent on any unspecified, undefined, or implementation-defined behavior, ... ... A conforming hosted implementation shall accept any strictly conforming program.