关闭文件

在 C++中很少需要显式关闭文件，因为文件流将自动在其析构函数中关闭其关联文件。但是，你应该尝试限制文件流对象的生命周期，这样它就不会使文件句柄保持打开的时间超过必要的时间。例如，这可以通过将所有文件操作放入自己的范围（{}）来完成：

std::string const prepared_data = prepare_data();
{
    // Open a file for writing.
    std::ofstream output("foo.txt");

    // Write data.
    output << prepared_data;
}  // The ofstream will go out of scope here.
   // Its destructor will take care of closing the file properly.

只有在以后想要重用相同的 fstream 对象但不想在两者之间保持文件打开时，才需要显式调用 close()：

// Open the file "foo.txt" for the first time.
std::ofstream output("foo.txt");

// Get some data to write from somewhere.
std::string const prepared_data = prepare_data();

// Write data to the file "foo.txt".
output << prepared_data;

// Close the file "foo.txt".
output.close();

// Preparing data might take a long time. Therefore, we don't open the output file stream
// before we actually can write some data to it.
std::string const more_prepared_data = prepare_complex_data();

// Open the file "foo.txt" for the second time once we are ready for writing.
output.open("foo.txt");

// Write the data to the file "foo.txt".
output << more_prepared_data;

// Close the file "foo.txt" once again.
output.close();