Question

I am using the gcc compiler for compiling C programs. How can I measure the exact CPU time required by a certain portion of C code or by a particular statement for its execution?

Answer 1

If a crude counter (~20ms resolution) is acceptable, this is my standard hacro:

#include <ctime>
#define CLOCK_TICK(acc, ctr)  ctr = std::clock()
#define CLOCK_TOCK(acc, ctr)  acc += (std::clock() - ctr)
#define CLOCK_RESET(acc) acc = 0
#define CLOCK_REPORT(acc) (1000. * double(acc) / double(CLOCKS_PER_SEC))

static std::clock_t tacc, tctr;

Usage:

CLOCK_TICK(tacc, tctr);
do_something_critical();
CLOCK_TOCK(tacc, tctr);

std::cout << "This took " << CLOCK_REPORT(tacc) << "ms.\n";

In C++11 you can use <chrono> features to get higher-resolution clocks.