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#include <stdio.h> #include <tchar.h> #include <iostream> #include <string> #include <Windows.h> using namespace std; #pragma comment(lib, "winmm.lib") int StringCompare(){ string strSource = "hello world!"; string strDest = "I am a luck dog!"; LARGE_INTEGER m_liPerfFreq = { 0 }; QueryPerformanceFrequency(&m_liPerfFreq); LARGE_INTEGER m_liPerfStart = { 0 }; QueryPerformanceCounter(&m_liPerfStart); for (int i = 0; i < 1e8; ++i) strSource == strDest; LARGE_INTEGER liPerfNow = { 0 }; QueryPerformanceCounter(&liPerfNow); int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * 1000) / m_liPerfFreq.QuadPart); cout << time << endl; return 0; } int CharCompare(){ char str1[100] = "hello world!"; char str2[100] = "I am a luck dog!"; LARGE_INTEGER m_liPerfFreq = { 0 }; QueryPerformanceFrequency(&m_liPerfFreq); LARGE_INTEGER m_liPerfStart = { 0 }; QueryPerformanceCounter(&m_liPerfStart); for (int i = 0; i < 1e8; ++i) strcmp(str1, str2); LARGE_INTEGER liPerfNow = { 0 }; QueryPerformanceCounter(&liPerfNow); int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * 1000) / m_liPerfFreq.QuadPart);//单位精确到毫秒，要是不乘以1000则就是秒 cout << time << endl; return 0; } int _tmain(int argc, _TCHAR* argv[]){ StringCompare(); CharCompare(); return 0; }
去掉10的8次方for循环的影响
#include <stdio.h> #include <tchar.h> #include <iostream> #include <string> #include <Windows.h> using namespace std; #pragma comment(lib, "winmm.lib") int StringCompare(){ string strSource = "hello world!"; string strDest = "I am a luck dog!"; LARGE_INTEGER m_liPerfFreq = { 0 }; QueryPerformanceFrequency(&m_liPerfFreq); LARGE_INTEGER m_liPerfStart = { 0 }; QueryPerformanceCounter(&m_liPerfStart); for (int i = 0; i < 1e8; ++i) ;//strSource == strDest; LARGE_INTEGER liPerfNow = { 0 }; QueryPerformanceCounter(&liPerfNow); int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * 1000) / m_liPerfFreq.QuadPart); cout << time << endl; return 0; } int CharCompare(){ char str1[100] = "hello world!"; char str2[100] = "I am a luck dog!"; LARGE_INTEGER m_liPerfFreq = { 0 }; QueryPerformanceFrequency(&m_liPerfFreq); LARGE_INTEGER m_liPerfStart = { 0 }; QueryPerformanceCounter(&m_liPerfStart); for (int i = 0; i < 1e8; ++i) ;//strcmp(str1,str2); LARGE_INTEGER liPerfNow = { 0 }; QueryPerformanceCounter(&liPerfNow); int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * 1000) / m_liPerfFreq.QuadPart);//单位精确到毫秒，要是不乘以1000则就是秒 cout << time << endl; return 0; } int _tmain(int argc, _TCHAR* argv[]){ StringCompare(); CharCompare(); return 0; }
windows里
LARGE_INTEGER
QueryPerformanceCounter
QueryPerformanceFrequency
timeGettime
综上所述： 当达到10的8次方这个数量级时，string的相等操作确实是要比strcmp耗时，虽然string的重载的相等操作是memcmp内存的比较，但是之前还是有很多的判断的；
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原文地址：http://www.cnblogs.com/panyingying/p/5104878.html
