mic@mic-nb /tmp $ cat main.cpp

namespace math {
#include <math.h>
}

int main() {
    return math::expf(5);
}
mic@mic-nb /tmp $ g++ main.cpp
mic@mic-nb /tmp $ ./a.out; echo $?
148
mic@mic-nb /tmp $ g++ main.cpp -nostdlib
/usr/bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000000400144
/tmp/ccSX0iir.o: In function `main':
main.cpp:(.text+0xd): undefined reference to `expf'
collect2: error: ld returned 1 exit status