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C/C++的8种时间度量方式以及代码片段( 二 )

C++


time(&begin);
int iterations = 1000*1000*1000;
for (int i=0; i
sum += add;
add /= 2.0;
// Stop measuring time and calculate the elapsed time
time(&end);
time_t elapsed = end - begin;
printf("Result: %.20fn", sum);
printf("Time measured: %ld seconds.n", elapsed);
return 0;
time_t实际上就是alias long int ， 因此你可以直接用printf()和cout进行打印
5.#include clock() - for Linux & Windows, CPU time on Linux, Wall time on Windows, seconds
clock()会返回在程序开始执行之后的clock ticks. 你可以通过他去除以CLOCKS_PER_SEC(在自己的Linux虚拟机测下来这个值是1000000) ， 你会得到程序执行了多少时间(s).但是这对于不同的操作系统 ， 行为是不一样的 ， 比如在Linux,你得到的是CPU time ， 在Windows,你得到的是Wall time.因此你需要特别小心
#include
#include
int main () {
double sum = 0;
double add = 1;
// Start measuring time
clock_t start = clock();
int iterations = 1000*1000*1000;
for (int i=0; i
sum += add;
add /= 2.0;
// Stop measuring time and calculate the elapsed time
clock_t end = clock();
double elapsed = double(end - start)/CLOCKS_PER_SEC;
printf("Result: %.20fn", sum);
printf("Time measured: %.3f seconds.n", elapsed);
return 0;
clock_t本身也是long int, 所以当你用除法去除以CLOCKS_PER_SEC的时候 ， 你需要先转换到double ， 否则你会因为整除而失去信息
6.#include clock_gettime() - for Linux Only,Wall time / CPU time ， nanoseconds
这个API是比较强大的 ， 因为他既可以用来测Wall time又可以用来测CPU time,同时他支持nanoseconds级别 。但是他唯一的不好的地方就是他只适用于Unix.你可以通过flag来控制测量wall time或者是CPU time ， 通过对应的CLOCK_PROCESS_CPUTIME_ID(wall time)或者CLOCK_REALTIME(CPU time)
#include
#include
int main () {
double sum = 0;
double add = 1;
【C/C++的8种时间度量方式以及代码片段】// Start measuring time
struct timespec begin, end;
clock_gettime(CLOCK_REALTIME, &begin);
int iterations = 1000*1000*1000;
for (int i=0; i
sum += add;
add /= 2.0;
// Stop measuring time and calculate the elapsed time
clock_gettime(CLOCK_REALTIME, &end);
long seconds = end.tv_sec - begin.tv_sec;
long nanoseconds = end.tv_nsec - begin.tv_nsec;
double elapsed = seconds + nanoseconds*1e-9;
printf("Result: %.20fn", sum);
printf("Time measured: %.3f seconds.n", elapsed);
return 0;
除了CLOCK_REALTIME和CLOCK_PROCESS_CPUTIME_ID之外 ， 你可以使用其他的clock types. 这里的timespec跟gettimeofday()的timeval很类似 ， 但是timeval包含的是microseconds,而timespec包含的是nanoseconds
7.#include GetTickCount64() - for Windows Only, milliseconds
返回当系统开机之后的millseconds毫秒个数 ， 同样这里也有32位的版本GetTickCount(), 但是他会把时间限制在49.71 days,所以用64 bit都是比较好的
#include
#include
int main () {
double sum = 0;
double add = 1;
// Start measuring time
long long int begin = GetTickCount64();
int iterations = 1000*1000*1000;
for (int i=0; i
sum += add;
add /= 2.0;
// Stop measuring time and calculate the elapsed time
long long int end = GetTickCount64();
double elapsed = (end - begin)*1e-3;
printf("Result: %.20fn", sum);
printf("Time measured: %.3f seconds.n", elapsed);
return 0;
8.#include GetProcessTimes() - for Windows Only(但是这时唯一可以在Windows上测量CPU time的方法), CPU time
原理本身比较复杂 ， 如果有兴趣可以自己找资料继续阅读
#include
#include
double get_cpu_time(){
FILETIME a,b,c,d;
if (GetProcessTimes(GetCurrentProcess(),&a,&b,&c,&d) != 0){
// Returns total user time.
// Can be tweaked to include kernel times as well.
return
(double)(d.dwLowDateTime |
((unsigned long long)d.dwHighDateTime << 32)) * 0.0000001;
}else{
// Handle error
return 0;
int main () {
double sum = 0;
double add = 1;
// Start measuring time
double begin = get_cpu_time();
int iterations = 1000*1000*1000;
for (int i=0; i
sum += add;
add /= 2.0;
// Stop measuring time and calculate the elapsed time
double end = get_cpu_time();
double elapsed = (end - begin);
printf("Result: %.20fn", sum);


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