is memset() more efficient than for loop in C?

Question

is memset more efficient than for loop. so if i have

char x[500];
memset(x,0,sizeof(x));

or

char x[500];
for(int i = 0 ; i &         


        

Answer 1

The answer is 'it depends'. memset MAY be more efficient, or it may internally use a for loop. I can't think of a case where memset will be less efficient. In this case, it may turn into a more efficient for loop: your loop iterates 500 times setting a bytes worth of the array to 0 every time. On a 64 bit machine, you could loop through, setting 8 bytes (a long long) at a time, which would be almost 8 times quicker, and just dealing with the remaining 4 bytes (500%8) at the end.

EDIT:

in fact, this is what memset does in glibc:

http://repo.or.cz/w/glibc.git/blob/HEAD:/string/memset.c

As Michael pointed out, in certain cases (where the array length is known at compile time), the C compiler can inline memset, getting rid of the overhead of the function call. Glibc also has assembly optimized versions of memset for most major platforms, like amd64:

http://repo.or.cz/w/glibc.git/blob/HEAD:/sysdeps/x86_64/memset.S