errno - cppreference.com (original) (raw)

| | | | | -------------------------------------------- | | | | #define errno /* implementation-defined */ | | |

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 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

Possible output:

nan log(-1) failed: Numerical argument out of domain Or, in German, Das numerische Argument ist ausserhalb des Definitionsbereiches

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also