< cpp‎ | io‎ | c
Defined in header <cstdio>
void perror( const char *s );

Prints a textual description of the error code currently stored in the system variable errno to stderr.

The description is formed by concatenating the following components:

  • the contents of the null-terminated byte string pointed to by s (unless s is a null pointer)
  • ": "
  • implementation-defined error message describing the error code stored in errno. This message is identical to the output of std::strerror(errno).
  • '\n'.


s - pointer to a null-terminated string with explanatory message

Return value



#include <cmath>
#include <cerrno>
#include <cstdio>
int main()
    double not_a_number = std::log(-1.0);
    if (errno == EDOM) {
        std::perror("log(-1) failed");


log(-1) failed: Numerical argument out of domain

See also

macro which expands to POSIX-compatible thread-local error number variable
(macro variable)
returns a text version of a given error code
C documentation for perror