Complexity of strncmp in string.h

Question

I would like to know the time complexity of int strncmp(const char *__s1, const char *__s2, size_t __n) which is in the C library(string.h).

I have to study the complexity of my whole program which is calling strncmp thousands of time, I can't ignore this complexity.
Where can I find documentation about the complexity of c library function ?

Your can derive the answer yourself considering the linear operation of comparing one char after each other. — Wör Du Schnaffzig, Feb 12 '21 at 11:07
Time complexity of strcmp in character comparisons is `O(k)` where `k` is the length of the common prefix up to n, and `k <= max[n, l1, l2]` strictly — Antti Haapala -- Слава Україні, Feb 12 '21 at 11:10

score 1 · Accepted Answer · answered Feb 12 '21 at 11:16

The standard imposes no requirements on the complexity. That is entirely up to the implementation. But there's absolutely no reason to expect it to be anything else than O(__n)

It's trivial to write an implementation that satisfies O(__n), so there's no reason to suspect that a real implementation made by professionals is worse.
It's impossible to write an implementation that is better than O(__n), so that will not happen.

But if you want to be sure, you have to study the particular implementation you're using.

Complexity of strncmp in string.h

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