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 (until C++11) thread-local (since C++11) modifiable lvalue of type int.
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
.
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
See also
macros for standard POSIX-compatible error conditions (macro constant) | |
displays a character string corresponding of the current error to stderr (function) | |
returns a text version of a given error code (function) |