ifstream :: is_open vs ifstream :: fail？ [英] ifstream::is_open vs ifstream::fail?
问题描述
读取Savitch的 std :: ifstream :: fail 作为示例显示，以检查文件是否正确打开（ ifstream 或 ofstream ）。
Reading Savitch's Problem Solving in C++, std::ifstream::fail is shown as an example to check if a file has been correctly opened (ifstream or ofstream).
ve以前使用，因为它是我第一次显示， std :: ifstream :: is_open 执行相同的检查。
I've previously used, as it is what I was first shown, std::ifstream::is_open to perform the same check.
这是更好的做法？
或者在尝试打开后直接调用任何一个的情况下，它没有实际差别吗？ p>
Or in the case that either one is called directly after attempting to open, does it make no practical difference?
推荐答案
简介
std :: ifstream： ：fail 包括检查 std :: ifstream :: is_open ，但 std :: ifstream :: is_open 只检查是否可以创建文件的句柄。
INTRODUCTION
std::ifstream::fail includes checking std::ifstream::is_open, but std::ifstream::is_open only checks if it was possible to create a handle to the file.
std :: ifstream :: fail 可以返回 true ：ifstream :: is_open 返回 true ;它们不是互相排斥的。
std::ifstream::fail can return true, even if std::ifstream::is_open returns true; they are not the mutually exclusive.
.fail 将检查整体health >，这涉及诸如检查流当前进入了失败状态以尝试读取无效值，而 .is_open 将仅检查流是否当前附加到文件， .is_open 不在乎流是否处于失败状态，或不。
.fail will check the overall "health" of the stream, which involves things such as checking the stream has currently entered a fail state from trying to read an invalid value, whereas .is_open will only check if the stream is currently attached to a file, .is_open doesn't care if the stream is in a fail state, or not.
通常建议您依赖于 显式运算符bool（） 以查看流是否可以读取/写入。这包括检查流的整体健康。
Normally it's recommended to rely on the explicit operator bool () to see if a stream is ready to be read/written to. This includes checking the overall health of the stream.
我们可以在 some_stream / p>
Can we make another read/write operation on some_stream?
if (some_stream) {
// stream is alive and well
} else {
// something is wrong
}
如果你明确想看看是否有一些 fstream 实际上附加到一个文件，使用 is_open ，如果你想检查整体健康;使用 .fail 或依赖于流可转换为 bool 的事实。
If you explicitly would like to see if some fstream is actually attached to a file, use is_open, and if you want to check the overall health; use .fail or rely on the fact that a stream is convertiable to bool.
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