C++字符串连接

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字符串格式化

参照下面的文章

http://www.cnblogs.com/james6176/p/3222671.html

http://blog.csdn.net/yunhua_lee/article/details/6381876

结果修改代码windows+vs2010代码如下

#include <iostream>
#include <string>
#include <time.h>
#include <sstream>
#include <stdio.h>
#include <vector>
using namespace std;

#define OUT_IN_REPEATE_NUM 10000
#define IN_REPEATE_NUM 60

string s1="abcedfg";
string s2="hijklmn";
string s3="opqrst";

void plusTest(string& ret)
{
    for(int i=0; i<IN_REPEATE_NUM; i++)
    {
        ret += s1;
        ret += s2;
        ret += s3;
    }
}
void appendTest(string& ret)
{
    for(int i=0; i<IN_REPEATE_NUM; i++)
    {
        ret.append(s1);
        ret.append(s2);
        ret.append(s3);
    }
}
void sprintfTest(string& ret)
{
    const size_t length=26*IN_REPEATE_NUM;
    char tmp[length];
    char* cp = tmp;
    size_t strLength=s1.length()+s2.length()+s3.length();
    for(int i=0; i<IN_REPEATE_NUM; i++)
    {
        sprintf(cp,"%s%s%s", s1.c_str(), s2.c_str(),s3.c_str());
        cp+=strLength;
    }
    ret = tmp;
}

void ssTest(string& ret)
{
    stringstream ss;
    for(int i=0; i<IN_REPEATE_NUM; i++)
    {
        ss<<s1;
        ss<<s2;
        ss<<s3;
    }
    ret = ss.str();
}

string ss, plus, append, sprintf;
clock_t sTime, eTime;

    sTime = clock();
    for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
    {
        sprintf="";
        sprintfTest(sprintf);
    }
    eTime = clock();
    long SprintfTime = eTime-sTime;

    sTime = clock();
    for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
    {
        append="";
        appendTest(append);
    }
    eTime = clock();
    long AppendTime = eTime-sTime;

    sTime = clock();
    for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
    {
        ss="";
        ssTest(ss);
    }
    eTime = clock();
    long SsTime = eTime-sTime;

    sTime = clock();
    for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
    {
        plus="";
        plusTest(plus);
    }
    eTime = clock();
    long PlusTime = eTime-sTime;

    cout<<"PlusTime is :   "<<PlusTime<<endl;
    cout<<"AppendTime is : "<<AppendTime<<endl;
    cout<<"SsTime is :     "<<SsTime<<endl;
    cout<<"SprintfTime is :"<<SprintfTime<<endl;
    if(ss==sprintf && append==plus && ss==plus)
    {
        cout<<"They are same"<<endl;
    }
    else
    {
        cout<<"Different!"<<endl;
        cout<<"Sprintf: "<<sprintf<<endl;
        cout<<"ss:        "<<ss<<endl;
        cout<<"Plus:     "<<plus<<endl;
        cout<<"Append:"<<append<<endl;
    }

system("pause");

测试发现不同的结果

debug下测试结果

PlusTme is : 610

AppendTime is:570

SsTim is :798

SprintfTime is:327

写文章前差点认为这就是最终结果，从而误导自己

release下测试结果

PlusTime is:15

AppendTime is:15

SsTime is:142

SprintfTime is :110

相差很多

结合以上得出结论std::string使用+=性能最好

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