c++ - 我对c++有关库有问题吗？

Question

我正在为学校学习C++。我正在使用Visual Studio编写C++，我正在尝试编译以下代码:

#include <iostream>
#include <stdio.h>

using namespace std;

int main()
{
    freopen("cd.inp", "r", stdin);
    freopen("cd.out", "w", stdout);
    int a, b;
    while (true){
        cin >> a >> b;
        cout << a << ' ' << b;
        break;
    }
    fclose(stdin);
    fclose(stdout);
}

我有这些错误:

Severity Code Description Project File Line Suppression StateError C4996 'freopen': This function or variable may be unsafe. Consider using freopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. clock_degrees F:\CODING\C++\clock_degrees\clock_degrees\clock_degrees.cpp 11

Severity Code Description Project File Line Suppression StateWarning C6031 Return value ignored: 'freopen'. clock_degrees F:\CODING\C++\clock_degrees\clock_degrees\clock_degrees.cpp 11

我现在该怎么办？
我也遇到了有关 scanf 和 printf 的问题，而不是 freopen 的问题。我以为问题来自 库。

Answer 1

您应该改为使用ifstream和ofstream:

#include <fstream>

// don't do using namespace std;
using std::ifstream;
using std::ofstream;
using std::ios_base;

int main() {
  ifstream in;
  ofstream out;
  in.exceptions(ios_base::failbit | ios_base::badbit);
  out.exceptions(ios_base::failbit | ios_base::badbit);
  try {
    in.open("cd.inp");
    int a, b;
    // The while loop is pointless
    in >> a >> b;
    out.open("cd.out");
    out << a << ' ' << b;
  } catch (ios_base::failure const& e) {
    // Error handling 
    return -1;
  } 
}

Why is “using namespace std;” considered bad practice?