当ifstream打开失败时如何获取错误消息

问题描述

ifstream f;
f.open(fileName);

if ( f.fail() )
{
    // I need error message here, like "File not found" etc. -
    // the reason of the failure
}

如何以字符串形式获取错误消息？

How to get error message as string?

推荐答案

每个失败的系统调用都会更新 errno 值。

Every system call that fails update the errno value.

因此，您可以通过使用类似以下内容来获得有关 ifstream 打开失败时会发生什么的更多信息：

Thus, you can have more information about what happens when a ifstream open fails by using something like :

cerr << "Error: " << strerror(errno);

但是，由于系统调用更新全局 errno value，在多线程应用程序中可能有问题，如果另一个系统调用触发执行 f.open 之间的错误， errno 。

However, since every system call updates the global errno value, you may have issues in a multithreaded application, if another system call triggers an error between the execution of the f.open and use of errno.

编辑（感谢Arne Mertz和其他人）：

Edit (thanks to Arne Mertz and other people in the comments):

e.what（）似乎最初是一种更C ++的方式 - ，但是这个函数返回的字符串是依赖于实现的（至少在G ++的libstdc ++中）这个函数有关错误背后的原因的有用信息...

e.what() seemed at first to be a more C++-idiomatically correct way of implementing this, however the string returned by this function is implementation-dependant and (at least in G++'s libstdc++) this function useful information about the reason behind the error...

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