macro

<cerrno>

int

Last error number

`int`

. Therefore, it can be both read and modified by a program.A program can also modify its value. In fact, if this variable is intended to be used for error checking after a library function call, it should be reset by the program to zero before the call (since any previous call to a library function may have altered its value).

The same header that declares

macro | meaning when errno is set to this |
---|---|

EDOM | Domain error: Some mathematical functions are only defined for certain real values, which is called its domain, for example the square root function is only defined for non-negative numbers, therefore the sqrt function sets errno to EDOM if called with a negative argument. |

ERANGE | Range error: The range of values that can be represented with a variable is limited. For example, mathematical functions such as pow can easily outbound the range representable by a floating point variable, or functions such as strtod can encounter sequences of digits longer than the range representable values. In these cases, errno is set to ERANGE. |

EILSEQ | Illegal sequence: Multibyte character sequence may have a restricted set of valid sequences. When a set of multibyte characters is translated by functions such as mbrtowc, errno is set to EILSEQ when an invalid sequence is encountered. |

The functions of the standard library may set

C++11 expands the basic set of values required to be defined in this header by including many names also available in POSIX environments, increasing the total number of portable

The particular error messages associated with values of

In C++,

`int`

object with external linkage.This is a requirement in libraries compliant with C11 and C++11 standards.