[Windows]

#include <windows.h>

DWORD begTick = GetTickCount();
foo();  
DWORD endTick = GetTickCount();
printf("%d\n", endTick - begTick);

[Linux]

#include <sys/time.h>

struct timeval begTick; gettimeofday(&begTick, NULL);
foo();  
struct timeval endTick; gettimeofday(&endTick, NULL);
printf("%ld\n", (endTick.tv_sec - begTick.tv_sec) * 1000 + (endTick.tv_usec - begTick.tv_usec) / 1000);

[Boost]

#include <boost/date_time/posix_time/posix_time.hpp>

boost::posix_time::ptime begTick(boost::posix_time::microsec_clock::local_time());
foo();  
boost::posix_time::ptime endTick(boost::posix_time::microsec_clock::local_time());
std::cout << boost::posix_time::to_simple_string(endTick - begTick) << std::endl;