perror

 

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Technical Specifications

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File input/output

Types and objects
FILE fpos_t      stdinstdoutstderr
Functions
File access fopenfopen_s (C11) freopenfreopen_s (C11) fwide (C95) setbuf setvbuf fclose fflush Direct input/output fread fwrite Unformatted input/output fgetc fgets fputc fputs getchar getsgets_s (until C11)(C11) putchar puts ungetc fgetwcgetwc (C95)(C95) fgetws (C95) fputwcputwc (C95)(C95) fputws (C95) getwchar (C95) putwchar (C95) ungetwc (C95) Formatted input scanffscanfsscanfscanf_sfscanf_ssscanf_s (C11)(C11)(C11) wscanffwscanfswscanfwscanf_sfwscanf_sswscanf_s (C95)(C95)(C95)(C11)(C11)(C11)     vscanfvfscanfvsscanfvscanf_svfscanf_svsscanf_s (C99)(C99)(C99)(C11)(C11)(C11) vwscanfvfwscanfvswscanfvwscanf_svfwscanf_svswscanf_s (C99)(C99)(C99)(C11)(C11)(C11)	Formatted output printffprintfsprintfsnprintfprintf_sfprintf_ssprintf_ssnprintf_s (C99)(C11)(C11)(C11)(C11) wprintffwprintfswprintfwprintf_sfwprintf_sswprintf_ssnwprintf_s (C95)(C95)(C95)(C11)(C11)(C11)(C11)     vprintfvfprintfvsprintfvsnprintfvprintf_svfprintf_svsprintf_svsnprintf_s (C99)(C11)(C11)(C11)(C11) vwprintfvfwprintfvswprintfvwprintf_svfwprintf_svswprintf_svsnwprintf_s (C95)(C95)(C95)(C11)(C11)(C11)(C11) File positioning ftell fgetpos fseek fsetpos rewind Error handling clearerr feof ferror perror Operations on files remove rename tmpfiletmpfile_s (C11) tmpnamtmpnam_s (C11)

 

Defined in header <stdio.h>
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 strerror(errno).

Parameters

s

-

pointer to a null-terminated string with explanatory message

Return value

(none)

Example

Run this code

#include <stdio.h>
 
int main(void)
{
    FILE *f = fopen("non_existent", "r");
    if (f == NULL) {
        perror("fopen() failed");
    } else {
        fclose(f);
    }
}

Possible output:

fopen() failed: No such file or directory

References

• C11 standard (ISO/IEC 9899:2011):

• 7.21.10.4 The perror function (p: 339)

• C99 standard (ISO/IEC 9899:1999):

• 7.19.10.4 The perror function (p: 305)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.9.10.4 The perror function

See also

strerrorstrerror_sstrerrorlen_s (C11)(C11)	returns a text version of a given error code (function)
C++ documentation for perror