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  • 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 = { 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; }

    image

    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;
    }

    image

    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;

    本文由博主(YinaPan)原创或者转载,如若转载请务必注明出处,谢谢合作!
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  • 原文地址:https://www.cnblogs.com/YinaPan/p/cpp_strcmp.html
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