程序代码：

// Note:Your choice is C++ IDE
#include <sstream>
#include <fstream>
#include <string>
#include <iostream>
#include <vector>
using namespace std;

int nCount = 0;

string& replaceAll(string& context, const string& from, const string& to)
{
    size_t lookHere = 0;
    size_t foundHere;
    while((foundHere = context.find(from, lookHere)) != string::npos)
    {
        nCount++;
        context.replace(foundHere, from.size(), to);
    }
    return context;
}

int main()
{
    ifstream ifile("g:\\123.txt");
    string str;
    vector<string> text;
    string from;
    string to;
    int nSum = 0;
   
    cout<<"文本内容"<<str<<endl;
    while(getline(ifile, str))
    {
        cout<<str<<endl;
    }
    ifile.close();
    ifile.clear();
   
     cout<<"请输入要替换的内容:";
     cin>>from;
     cout<<"请输入要替换为的内容:";
     cin>>to;
   
    ifile.open("g:\\123.txt");
    while(getline(ifile, str))
    {
        replaceAll(str, from, to);
        nSum += nCount;
        text.push_back(str);
    }
   
    ifile.close();
    ifile.clear();
   
    cout<<"共修改"<<nSum<<"处"<<endl;
   
    if(text.size())
    {
        cout<<"替换后:"<<endl;
        ofstream ofile("g:\\123.txt");
        for(int i = 0; i != text.size(); ++i)
        {
            ofile<<text[i]<<endl;
            cout<<text[i]<<endl;
        }
        ofile.close();
        ofile.clear();
    }
    else
    {
        cout<<"没有找到可以替换的!";
        while(getline(ifile, str))
        {
            cout<<str<<endl;
        }
    }
  
    return 0;
}