C++字符串替換

第一個方法是查的，百度一下挺多的···
6秒左右吧，慢了然後自己寫了第二個，也是6s多····························

有好辦法的老鐵留言指教下，在此先謝過了！

#include <iostream>

using namespace std;

//轉載，網上太多了，不知道原作者是誰了···
void string_replace(string & strBig, const string & strsrc, const string &strdst)
{
    string::size_type pos = 0;
    string::size_type srclen = strsrc.size();
    string::size_type dstlen = strdst.size();
    while ((pos = strBig.find(strsrc, pos)) != string::npos)
    {
        // 如果能找到 pos
        strBig.replace(pos, srclen, strdst);
        pos += dstlen;
    }
}

void stringReplace(string & strBig, const string & strSrc, const string & strDst) {
    int startPos = 0;

    int lenStrBig = strBig.length();
    int lenStrSrc = strSrc.length();
    bool equ = false;
    for (int i = 0; i < lenStrBig; ++i) {
        if (equ) break;
        for (int j = 0; j < lenStrSrc; ++j) {
            if (strBig[i] != strSrc[j]) break;
            else {
                if (j == 0) startPos = i;
                ++i;
            }
            if (j == lenStrSrc - 1) equ = true;
        }
    }

    int endPos = startPos + lenStrSrc;
    string fin = "\0";
    for (int i = 0; i < startPos; ++i)
        fin += strBig[i];

    fin += strDst;
    for (int i = endPos; i < lenStrBig; ++i)
        fin += strBig[i];

    strBig = fin;
}

int main()
{
    string str1, str2, str3;
    getline(cin, str1);
    getline(cin, str2);
    getline(cin, str3);

    string_replace(str1, str2, str3);

    stringReplace(str1, str2, str3);

    cout << str1;

    return 0;
}