I know we can use
perror()
in C to print errors. I was just wondering if there is a C++ alternative to this, or whether I have to include this (and therefore stdio.h) in my program. I am trying to avoid as many C functions as possible.
Thanks!
+5
A:
You could do something like:
std::cerr << strerror(errno) << std::endl;
That still ends up calling strerror, so you're really just substituting one C function for another. OTOH, it does let you write via streams, instead of mixing C and C++ output, which is generally a good thing. At least AFAIK, C++ doesn't add anything to the library to act as a substitute for strerror (other than generating an std::string, I'm not sure what it would change from strerror anyway).
Jerry Coffin
2010-07-23 17:47:57
A C++ version of `strerror` which would return a `std::string` would presumably also be thread-safe, which would be a nice improvement.
Tyler McHenry
2010-07-23 18:22:42
@Tyler: Well, that's certainly possible, and would be a handy improvement. OTOH, getting thread safety out of anything that uses `errno` almost unavoidably uses thread local storage anyway (i.e., about the same as it takes to make `strerror` thread safe).
Jerry Coffin
2010-07-23 18:29:57
@Jerry I'm not sure about other threading frameworks, but POSIX threads guarantee that `errno` is thread-local automatically. The problem with `strerror` is that it returns a pointer to a static buffer that is not thread-local.
Tyler McHenry
2010-07-23 21:28:34
@Tyler: My point was that to make `errno` work, you need to have and use TLS anyway, and once you're using it, you might as well use it for `strerror`'s buffer too.
Jerry Coffin
2010-07-23 22:46:59
@Tyler McHenry: Having an error-message-creation-function that creates a std::string would be very inappropriate. How would that function work if it would try to report "out of memory"? I would say that an error-function that takes a char* buffer with a given size would be the most appropriate. It's also "thread-safe".
Simon
2010-07-26 14:35:32
@Simon And there exists such a thing (`perror_r`), although you do have a point about out-of-memory errors.
Tyler McHenry
2010-07-26 14:53:24
Oh nice, I didn't know about perror_r. Thanks!
Simon
2010-07-26 15:08:45
Sagar
2010-07-26 15:37:48
+1
A:
You could use the boost::system_error::error_code class.
#include <boost/system/system_error.hpp>
#include <cerrno>
#include <iostream>
void
PrintError(
const std::string& message,
int error
)
{
std::cerr << message << ": " <<
boost::system::error_code(
error,
boost::system::get_system_category()
).message()
<< std::endl;
}
int
main()
{
PrintError( "something went wrong!", EINVAL );
return 0;
}
it's a tad verbose, and somewhat overkill if you aren't already using the boost_system library.
Sam Miller
2010-07-23 18:08:19
Wouldn't that be pretty bad if you happen to do PrintError("We ran out of memory!", EINVAL); when you discover that you failed to do a memory-allocation?
Simon
2010-07-26 14:36:49
Can't actually use the boost library. This has to be as 'plain' (for lack of a better term) as possible. Trying not to include any 3rd party stuff. Thanks though!
Sagar
2010-07-26 15:35:00