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errno(5)
NAME
  errno - Returns error condition value

SYNOPSIS
  #include <errno.h>

DESCRIPTION
  The errno external variable contains the most recent error condition set by
  a function. The symbolic values for errno are listed in the intro reference
  page and in the ERRORS section of the individual reference pages for each
  function.

  The exec() functions set errno to a value of 0 (zero) after successful
  completion. Typically, other functions only set errno to a nonzero value.

EXAMPLES
  The following program uses the value of errno to determine why the
  requested file could not be opened.  If errno has one of the two tested
  values, the program prints an appropriate message; otherwise, the program
  uses the error() function to print out the appropriate message. This
  program does not have to set errno to a value of 0 (zero) because errno is
  tested only if the open() function has failed.

       #include <errno.h>
       #include <stdio.h>
       #include <string.h>
       #include <fcntl.h>
       #include <sys/stat.h>
       #include <sys/types.h>
       #define SLENGTH 80

       main()
       {
	   char filespec[SLENGTH], *eol;
	   int opret;
	   while (TRUE) {
	       printf("Enter file to be checked: ");
	       fgets(filespec, SLENGTH, stdin);
	       if ((eol = strchr(filespec, '\n')) != NULL) {
		   *eol = '\0';	 /* Replace newline with null */
		   if (*filespec == '\0') return; /* exit program */
		   opret = open(filespec,O_RDONLY,0);
		   if (opret > 0)
		     printf("%s: File exists\n",filespec);
		   else if (errno == ENOENT)
		     printf("%s: File does not exist\n",filespec);
		   else if (errno == ENOTDIR)
		     printf("%s: Prefix in path is not a directory\n",
		       filespec);
		   else
		     perror(filespec);

	       } else		/* Line entered too long */
		 printf("Line entered is too long\n");
	   }
       }

NOTES
  To ensure that your programs are portable, you should not explicitly
  declare errno to be an extern int in your program.  You should rely on the
  type int declaration in the <errno.h> include file.

  AES Support Level:
      Full use.

SEE ALSO
  Functions: intro(2), perror(3), strerror(3)

Index for Section 5

Alphabetical listing for E

Top of page