C namespace using structures

You can simulate namespaces in C as follows:

#include <stdio.h>
#include <math.h>

struct math_namespace {
    double (*sin)(double);
};
const struct math_namespace math = {sin};

int main() {    
    printf("%f\n", math.sin(3));

    return 0;
}

Are there any flaws in this, or just a situation where the prefix makes more sense? It just seems that doing it so clean.