strcmp和==比较

本文由博主(YinaPan)原创，转载请注明出处：http://www.cnblogs.com/YinaPan/p/cpp_strcmp.html 
#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 = {  };
    QueryPerformanceFrequency(&m_liPerfFreq);

    LARGE_INTEGER m_liPerfStart = {  };
    QueryPerformanceCounter(&m_liPerfStart);

    for (int i = ; i < 1e8; ++i)
        strSource == strDest;

    LARGE_INTEGER liPerfNow = {  };
    QueryPerformanceCounter(&liPerfNow);

    int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * ) / m_liPerfFreq.QuadPart);
    cout << time << endl;

    return ;

}

int CharCompare(){

    char str1[] = "hello world!";
    char str2[] = "I am a luck dog!";

    LARGE_INTEGER m_liPerfFreq = {  };
    QueryPerformanceFrequency(&m_liPerfFreq);

    LARGE_INTEGER m_liPerfStart = {  };
    QueryPerformanceCounter(&m_liPerfStart);

    for (int i = ; i < 1e8; ++i)
        strcmp(str1, str2);

    LARGE_INTEGER liPerfNow = {  };
    QueryPerformanceCounter(&liPerfNow);

    int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * ) / m_liPerfFreq.QuadPart);//单位精确到毫秒，要是不乘以1000则就是秒
    cout << time << endl;

    return ;
}

int _tmain(int argc, _TCHAR* argv[]){

    StringCompare();
    CharCompare();
    return ;
}

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 = {  };
    QueryPerformanceFrequency(&m_liPerfFreq);

    LARGE_INTEGER m_liPerfStart = {  };
    QueryPerformanceCounter(&m_liPerfStart);

    for (int i = ; i < 1e8; ++i)
        ;//strSource == strDest;

    LARGE_INTEGER liPerfNow = {  };
    QueryPerformanceCounter(&liPerfNow);

    int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * ) / m_liPerfFreq.QuadPart);
    cout << time << endl;

    return ;
}

int CharCompare(){

    char str1[] = "hello world!";
    char str2[] = "I am a luck dog!";

    LARGE_INTEGER m_liPerfFreq = {  };
    QueryPerformanceFrequency(&m_liPerfFreq);

    LARGE_INTEGER m_liPerfStart = {  };
    QueryPerformanceCounter(&m_liPerfStart);

    for (int i = ; i < 1e8; ++i)
        ;//strcmp(str1,str2);

    LARGE_INTEGER liPerfNow = {  };
    QueryPerformanceCounter(&liPerfNow);

    int time = (((liPerfNow.QuadPart - m_liPerfStart.QuadPart) * ) / m_liPerfFreq.QuadPart);//单位精确到毫秒，要是不乘以1000则就是秒
    cout << time << endl;

    return ;
}

int _tmain(int argc, _TCHAR* argv[]){

    StringCompare();
    CharCompare();

    return ;
}

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；