In GCC 4.4 and up you can use the following: #pragma GCC push_options #pragma GCC optimize ("O0") memset(a, 0, 3); #pragma GCC pop_options '

In GCC 4.4 and up you can use the following: #pragma GCC push_options #pragma GCC optimize ("O0") memset(a, 0, 3); #pragma GCC pop_options 'volatile' should also work, I don't see why there is any need to rewrite memset. Here is a related question on SO: http://stackoverflow.com/questions/2219829/how-to-prevent-gcc-optimizing-some-statements-in-c http://stackoverflow.com/questions/2219829/how-to-prevent-gc... Edit: buried at the bottom of that post is another method: __attribute__((optimize("O0")))