c++ - 在 C++ 中写入文本文件时使用布尔标志的问题

Question

我正在学习读/写文件的语法和细微差别。这是我的问题。如果我的代码基于用户标志 (write_outfile = true) 写入文件，那么我在最后关闭文件的尝试会导致“未定义标识符”错误。

但是，如果我在同一个“if”语句中打开然后关闭文件，那么一切都很好。

这是麻烦的代码片段：

#include <iostream>
#include <fstream>

int main()
  bool write_outfile = true;

  if (write_outfile)
  {
    ofstream outfile;
    outfile.open("output_test.txt");
    outfile << "This is my first text file written from C++.\n";
  }

// Do some other stuff here

  if (write_outfile)
  {
        outfile.close();
  }

Answer 1

ofstream outfile在最外层范围内声明。否则，它只在第一个 if 语句中定义。那是：

#include <iostream>
#include <fstream>

int main() {
  bool write_outfile = true;
  ofstream outfile;

  if (write_outfile)
  {
    outfile.open("output_test.txt");
    outfile << "This is my first text file written from C++.\n";
  }

// Do some other stuff here

  if (write_outfile)
  {
        outfile.close();
  }

}

Answer 2

if语句块引入了一个新范围。您outfile在该范围内创建，它在以下被销毁}。只需在块outfile外定义：if

bool write_outfile = true;

ofstream outfile;
if (write_outfile)
{
  outfile.open("output_test.txt");
  outfile << "This is my first text file written from C++.\n";
}
// ...