C++ 获取 std::fstream 失败错误消息和/或异常
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原文地址: http://stackoverflow.com/questions/839644/
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Get std::fstream failure error messages and/or exceptions
提问by sofr
I'm using fstream. Is there any way to get the failure message/exception?
我正在使用 fstream。有没有办法获得失败消息/异常？
For example if I'm unable to open the file?
例如，如果我无法打开文件？
采纳答案by sofr
From checking it out I found that also errnoand also GetLastError()do set the last error and checking them is quite helpful. For getting the string message use:
从检查出来我发现也errno还GetLastError()都设置了一个错误，并检查他们来说是非常有帮助的。要获取字符串消息，请使用：
strerror(errno);
回答by sofr
Streams by default do not throw exceptions on error, they set flags. You can make them throw exceptions by using the stream's exception() member function:
默认情况下，流不会在出错时抛出异常，它们会设置标志。您可以使用流的 exception() 成员函数使它们抛出异常：
ifstream ifs;
ifs.exceptions( std::ios::failbit ); // throw if failbit get set
Theoretically, you could then do something like this:
从理论上讲，您可以执行以下操作：
try {
int x;
ifs >> x;
}
catch( const std::exception & ex ) {
std::cerr << "Could not convert to int - reason is "
<< ex.what();
}
Unfortunately, the C++ Standard does not specify that thrown exceptions contain any error message, so you are in implementation specific territory here.
不幸的是，C++ 标准没有指定抛出的异常包含任何错误消息，因此您在这里处于特定于实现的领域。
回答by Doug
Short answer: no. Even checking errnoafter you detect failure (using e.g. bad(), fail()) after various operations doesn't reliably work. Creating an ifstream/ofstreamwrapping a file that can't be opened doesn't necessarily set a failure bit until you try to read, write, or close it.
简短的回答：没有。即使在各种操作errno后检测到失败（例如使用bad(), fail()）后进行检查也不能可靠地工作。创建ifstream/ofstream包装无法打开的文件不一定会设置失败位，直到您尝试读取、写入或关闭它。
Long answer: you can call ios::exceptions(ios_base::iostate)to request that ios_base::ios_failureexceptions be thrown when a corresponding bit (badbit, failbit, eofbit) is set, but this (at least on GNU and Microsoft C++ libraries) doesn't get you any more information than manually checking the bits, and ends up being largely pointless, IMHO.
长答案：您可以调用ios::exceptions(ios_base::iostate)请求ios_base::ios_failure在设置相应位（badbit、failbit、eofbit）时抛出异常，但这（至少在 GNU 和 Microsoft C++ 库上）不会比手动检查更多信息位，最终在很大程度上毫无意义，恕我直言。
