#include <string.h>
char *strerror(int errnum);
strerror maps the number in errnum to a message string. Typically, the values for errnum come from errno, but strerror can map any value of type int to a message.
strerror returns a pointer to the message string.
The program must not modify the returned message string. The message may be overwritten by a subsequent call to strerror.
strerror conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).