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Full Discussion: Hi errno in sys/stat.h
Top Forums Programming Hi errno in sys/stat.h Post 302095885 by hegemaro on Saturday 11th of November 2006 06:12:23 PM
Old 11-11-2006
Using the system errno is very important in C programming. All system calls will tell you there is an error by returning a -1, or NULL, or EOF, but only the errno variable, which is set by the system can tell you what the error is. To use it in a program, you need simply include the errno header file and define it as an external int.

Code:
#include <stdio.h>
#include <errno.h>

    extern int        errno;

int main ( int argc , char * const argv [ ] , char * const envp [ ] )
{
    return (0);
}

You can also get a textual description using the perror(3C) function.

Code:
#include <stdio.h>
#include <errno.h>
#include <strings.h>
#include <sys/types.h>
#include <sys/stat.h>

    extern int        errno;


int main ( int argc , char * const argv [ ] , char * const envp [ ] )
{
    char *          cpString = "/file/that/is/not/there";
    struct stat     Status;

    if ( stat (cpString, &Status) == -1 )
    {
        perror (cpString);
    }

    return (0);
}

# ./a.out
/file/that/is/not/there: No such file or directory

A little function I use in most of my programs for displaying system error messages follows. It uses the string function strerror(3C) to display a text message for any given errno value.

Code:
#include <stdio.h>
#include <errno.h>
#include <strings.h>
#include <sys/types.h>
#include <sys/stat.h>

    extern int        errno;


    int syserr ( const char Format [ ] , char * S1 , char * S2 )
    {
        fprintf (stderr, Format, ( S1 ? S1 : "" ), ( S2 ? S2 : "" ));
        fprintf (stderr, " (%d, %s)\n", errno,
                 ( (S1 = strerror (errno)) ? S1 : "undefined error" ));

        return (errno);
    }

    

int main ( int argc , char * const argv [ ] , char * const envp [ ] )
{
    char *          cpString = "/file/that/is/not/there";
    struct stat     Status;

    if ( stat (cpString, &Status) == -1 )
    {
        syserr ("Unable to %s %s", "status", cpString);
    }

    return (0);
}


# ./a.out
Unable to status /file/that/is/not/there (2, No such file or directory)

 

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LEARN ABOUT OSX

isaexec

isaexec(3C)						   Standard C Library Functions 					       isaexec(3C)

NAME

       isaexec - invoke isa-specific executable

SYNOPSIS

       #include <unistd.h>

       int isaexec(const char *path, char *const argv[], char *const envp[]);

DESCRIPTION

       The isaexec() function takes the path specified as path and breaks it into directory and file name components. It enquires from the running
       system the list of supported instruction set architectures; see isalist(5). The function traverses the list for an executable file in named
       subdirectories of the original directory.  When such a file is located, execve() is invoked with argv[] and envp[]. See exec(2).

RETURN VALUES

       If no file is located, isaexec() returns ENOENT. Other return values are the same as for execve().

EXAMPLES

       Example 1: Example of isaexec() function.

       On a system whose isalist is

       sparcv7 sparc

       the program

       int
       main(int argc, char *argv[], char *envp[])
       {
	       return (isaexec("/bin/thing", argv, envp));
       }

       will  look  first  for  an  executable  file  named  /bin/sparcv7/thing, then for an executable file named /bin/sparc/thing. It will invoke
       execve() on the first executable file it finds named thing.

       On that same system, a program called /u/bin/tofu can cause either /u/bin/sparcv7/tofu or /u/bin/sparc/tofu to be invoked using the follow-
       ing code:

       int
       main(int argc, char *argv[], char *envp[])
       {
		     return (isaexec(getexecname(), argv, envp));
       }

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Safe			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Stable			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       exec(2), getexecname(3C), attributes(5), isalist(5)

SunOS 5.10							    20 Mar 1998 						       isaexec(3C)
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