有没有人知道哪里出错

一定要写这么复杂么
试试

#include <iostream>
#include <fstream>
using namespace std;

int main(int argc, char const *argv[])
{
    ifstream fd;
    fd.open("output.txt", ios::in);
    char buf[1024];
    int line = 0;
    while (fd.getline(buf, sizeof(buf)))
    {
        cout << line << " : " << buf << endl;
        line++;
    }
}