What is errno?
errno is a positive integer.errno is normally a global integer variable indicating the exact type of errors for most functions.errno may also be a macro expanded into a function.
What is errno in a POSIX threaded program?
errno is defined as a macro expanded into a function __errno which returns the pointer to the actual errno variable.- POSIX threaded function will return an error number same as the type of
errno, which indicates the exact type of error.
The definition of errno
#if defined(_REENTRANT) || _POSIX_C_SOURCE - 0 >= 199506L
extern int *___errno();
#define errno (*(___errno()))
#else
extern int errno;
/* ANSI C++ requires that errno be a macro */
#if __cplusplus >= 199711L
#define errno errno
#endif
#endif /* defined(_REENTRANT) */
