errno
From cppreference.com
| Defined in header
<cerrno>
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| #define errno /*implementation-defined*/
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errno is a preprocessor macro used for error indication.
| It expands to a static modifiable lvalue of type int. | (until C++11) |
| It expands to a thread-local modifiable lvalue of type int. | (since C++11) |
Several standard library functions indicate errors by writing positive integers to errno. Typically, the value of errno is set to one of the error codes, listed in <cerrno> as macro constants that begin with the letter E, followed by uppercase letters or digits.
The value of errno is 0 at program startup, and although library functions are allowed to write positive integers to errno whether or not an error occurred, library functions never store 0 in errno.
[edit] Example
Run this code
#include <iostream> #include <cmath> #include <cerrno> #include <cstring> #include <clocale> int main() { double not_a_number = std::log(-1.0); if (errno == EDOM) { std::cout << "log(-1) failed: " << std::strerror(errno) << '\n'; std::setlocale(LC_MESSAGES, "de_DE.utf8"); std::cout << "Or, in German, " << std::strerror(errno) << '\n'; } }
Possible output:
log(-1) failed: Numerical argument out of domain Or, in German, Das numerische Argument ist ausserhalb des Definitionsbereiches
[edit] See also
| macros for standard POSIX-compatible error conditions (macro constant) |
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| displays a character string corresponding of the current error to stderr (function) |
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| returns a text version of a given error code (function) |