#include <isotream>
#include <fstream>
#include <string>
using namespace std;
int readFile(char fileName[]) //fileName是需要处理的文件名
{ ifstream in(fileName);
if (!in) { cerr << "Cannot open the file:" << fileName << endl;
exit(EXIT_FAILURE); }
string str = "";
while (getline(in,str))
{ //调用str.substr()截取三个字符进行处理 }
in.close(); }