c++拼接字符串效率比较（+=、append、stringstream、sprintf）

wuxinit_ 2021-09-03

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

c++拼接字符串效率比较（+=、append、stringstream、sprintf）

最近写的程序用到大量拼接字符串，为了提高拼接效率，比较了一下+=、append、stringstream、sprintf四种拼接字符串的方法。

测试方法

比较方法是写了4个函数，分别用+=、append、stringstream、sprintf的方式来拼接字符串，拼接方法是将 s1="abcedfg"，s2="hijklmn"，s3="opqrst"三个字符串拼接到一起，总共循环60次。然后在main函数中依次调用这4 个函数，并打时间戳来计时。为了使时间差异更明显，可以取循环N（N可以为100或是1000000等）次调用的时间。代码如下：

  1 #include <iostream>
  2 #include <string>
  3 #include <sys/time.h>
  4 #include <sstream>
  5 #include <stdio.h>
  6 using namespace std;
  7 #define OUT_IN_REPEATE_NUM 10000
  8 #define IN_REPEATE_NUM 60
  9 
 10 string s1="abcedfg";
 11 string s2="hijklmn";
 12 string s3="opqrst";
 13 void  plusTest(string& ret)
 14 {
 15     for(int i=0; i<IN_REPEATE_NUM; i++)
 16     {
 17         ret += s1;
 18         ret += s2;
 19         ret += s3;
 20     }
 21 }
 22 void  appendTest(string& ret)
 23 {
 24     for(int i=0; i<IN_REPEATE_NUM; i++)
 25     {
 26         ret.append(s1);
 27         ret.append(s2);
 28         ret.append(s3);
 29     }
 30 }
 31 void sprintfTest(string& ret)
 32 {
 33     const size_t length=26*IN_REPEATE_NUM;
 34     char tmp[length];
 35     char* cp = tmp;
 36     size_t strLength=s1.length()+s2.length()+s3.length();
 37     for(int i=0; i<IN_REPEATE_NUM; i++)
 38     {
 39         sprintf(cp,"%s%s%s", s1.c_str(), s2.c_str(),s3.c_str());
 40         cp+=strLength;
 41     }
 42     ret = tmp;
 43 }
 44 
 45 void  ssTest(string& ret)
 46 {
 47     stringstream ss;
 48     for(int i=0; i<IN_REPEATE_NUM; i++)
 49     {
 50         ss<<s1;
 51         ss<<s2;
 52         ss<<s3;
 53     }
 54     ret = ss.str();
 55 }
 56 int main() {
 57     string ss, plus, append, sprintf;
 58     struct timeval sTime, eTime;
 59 
 60     gettimeofday(&sTime, NULL);
 61     for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
 62     {
 63         sprintf="";
 64         sprintfTest(sprintf);
 65     }
 66     gettimeofday(&eTime, NULL);
 67     long SprintfTime = (eTime.tv_sec-sTime.tv_sec)*1000000+(eTime.tv_usec-sTime.tv_usec); //exeTime 单位是微秒
 68 
 69     gettimeofday(&sTime, NULL);
 70     for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
 71     {
 72         append="";
 73         appendTest(append);
 74     }
 75     gettimeofday(&eTime, NULL);
 76     long AppendTime = (eTime.tv_sec-sTime.tv_sec)*1000000+(eTime.tv_usec-sTime.tv_usec); //exeTime 单位是微秒
 77 
 78     gettimeofday(&sTime, NULL);
 79     for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
 80     {
 81         ss="";
 82         ssTest(ss);
 83     }
 84     gettimeofday(&eTime, NULL);
 85     long SsTime = (eTime.tv_sec-sTime.tv_sec)*1000000+(eTime.tv_usec-sTime.tv_usec); //exeTime 单位是微秒
 86 
 87     gettimeofday(&sTime, NULL);
 88     for(int i=0; i<OUT_IN_REPEATE_NUM; i++)
 89     {
 90         plus="";
 91         plusTest(plus);
 92     }
 93     gettimeofday(&eTime, NULL);
 94     long PlusTime = (eTime.tv_sec-sTime.tv_sec)*1000000+(eTime.tv_usec-sTime.tv_usec); //exeTime 单位是微秒
 95 
 96     cout<<"PlusTime is :   "<<PlusTime<<endl;
 97     cout<<"AppendTime is : "<<AppendTime<<endl;
 98     cout<<"SsTime is :     "<<SsTime<<endl;
 99     cout<<"SprintfTime is :"<<SprintfTime<<endl;
100     if(ss==sprintf && append==plus && ss==plus)
101     {
102         cout<<"They are same"<<endl;
103     }
104     else
105     {
106         cout<<"Different!"<<endl;
107         cout<<"Sprintf: "<<sprintf<<endl;
108         cout<<"ss:        "<<ss<<endl;
109         cout<<"Plus:     "<<plus<<endl;
110         cout<<"Append:"<<append<<endl;
111     }
112 
113 }