std::perror(3)

NAME
std::perror - std::perror

Synopsis
   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, followed by ":
       " (unless s is a null pointer or the character pointed to by s is the null
       character).
     * implementation-defined error message string describing the error code stored in
       errno, followed by '\n'. The error message string is identical to the result of
       std::strerror(errno).

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

Return value
   (none)

Example
// Run this code
 #include <cerrno>
 #include <cmath>
 #include <cstdio>
 int main()
 {
     double not_a_number = std::log(-1.0);
     if (errno == EDOM)
         std::perror("log(-1) failed");
     std::printf("%f\n", not_a_number);
 }

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

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