Re: [boost] [system] error_code_test.cpp does not account for implementation-specific behaviour of strerror()

From: Beman Dawes (bdawes_at_[hidden])
Date: 2007-11-05 17:43:30

Boris Gubenko wrote:
> Test error_code_test[_dll] fails on HP-UX and AIX and I'd expect it to
> fail on Tru64 also (Tru64 results are currently not on the web).
> 
> The test checks message for error code -1 in both system and posix category
> and expects it to be "Unknown error". For system category:
> 
>   ec = error_code( -1, system_category );
>   std::cout << "error_code message for -1 is \"" << ec.message() << "\"\n";
>   BOOST_CHECK( ec.message().substr( 0, 13) == "Unknown error" );
> 
> IIUC, the assumption is that strerror(invalid-error-code) either returns
> a pointer to a string starting with "Unknown error", which is the case on
> Linux -- see below, or returns a null pointer in which case
> libs/system/src/error_code.cpp maps it to "Unknown error" string:
> 
>       const char * c_str = std::strerror( ev );
>       return std::string( c_str ? c_str : "Unknown error" );
> 
> The problem with this assumption is that there is no requirement in the C
> standard that the message string generated by strerror() for an invalid
> error code starts with "Unknown error" -- see excerpt from C99 below. For
> example, on HP-UX, strerror() returns an empty string and on Tru64 it
> returns "Error -1 occurred."
> 
> As for the null pointer, strerror() cannot return it -- again, see excerpt
> from C99 below. X/Open explicitly states that strerror() may signal error
> by setting errno, but not by returning any particular value:
> 
>   "
>   Upon successful completion, strerror() returns a pointer to the
>   generated message string. On error errno may be set, but no return
>   value is reserved to indicate an error.
>   "
> 
> It does not mean that error_code.cpp should not check for a null pointer
> as a precaution against non-conformant implementation of strerror().

It's in there because that's what Microsoft does, and I happened to 
start testing on Windows.

> 
> In libs/system/test/error_code_test.cpp, the check for the message
> string corresponding to error code -1 should either be conditionalized
> for different platforms or removed.

I think it should be conditional for various platforms. The test was 
added because of a reported crash, so I really do want to continue to do 
some testing of the return. But it really does need to be conditional.

Thanks,

--Beman