文本中删除不含关键字符串的行

#include <string> 
#include <fstream> 
#include <iostream>

using namespace std;

const string sourceFile="source.txt";        //源文件路径
const string resultFile="result.txt";        //结果文件路径
const string keyStr="a";            //关键字符串

int _tmain(int argc, _TCHAR* argv[])
{
    string str;
    ifstream fin(sourceFile);
    ofstream fout(resultFile);

    if(fin.fail())
    {
        cout<<"source file open failed!";
        return 1;
    }


    while ( getline(fin,str))        //按行读取，
    {
        if( str.find(keyStr,0)!=string::npos )        //查找关键字符串，
            fout<<str<<"\n";
    }

    return 0;
}