用于守护进程的出错处理函数

/*

* Error routines for programs that can run as a daemon.

*/



#include "apue.h"

#include <errno.h>    /* for definition of errno */

#include <stdarg.h>    /* ISO C variable arguments */

#include <syslog.h>



static void log_doit(int, int, const char *, va_list ap);



/*

* Caller must define and set this: nonzero if

* interactive, zero if daemon

*/

extern int log_to_stderr;;



/*

* Initialize syslog(), is running as daemon.

*/

void 

log_open(const char *ident, int option, int facility)

{

    if(log_to_stderr == 0)

        openlog(ident, option, facility);

}



/*

* Nonfatal error related to a system call.

* Print a message with the system's errno value and return.

*/

void 

log_ret(const char *fmt, ...)

{

    va_list        ap;

    va_start(ap, fmt);

    log_doit(1, LOG_ERR, fmt, ap);

    va_end(ap);

}



/*

* Fatal error realted to a system call.

* Print a message and terminate.

*/

void

log_sys(const char *fmt, ...)

{

    va_list        ap;

    

    va_start(ap, fmt);

    log_doit(1, LOG_ERR, fmt, ap);

    va_end(ap);

    exit(2);

}



/*

* Nonfatal error unrelated to a system call.

* Print a message and return.

*/

void

log_msg(const char *fmt, ...)

{

    va_list        ap;

    

    va_start(ap, fmt);

    log_doit(0, LOG_ERR, fmt, ap);

    va_end(ap);

}



/*

* Fatal error unrelated to a system call.

* Print a message and terminate.

*/

void

log_quit(const char *fmt, ...)

{

    va_list        ap;

    

    va_start(ap, fmt);

    log_doit(0, LOG_ERR, fmt, ap);

    va_end(ap);

    exit(2);

}



/*

* Print a message and return to caller.

* Caller specifies "errnoflag" and "priority". 

*/

static void

log_doit(int errnoflag, int priority, const char *fmt, va_list ap)

{

    int     errno_save;

    char     buf[MAXLINE];



    errno_save = errno;    /* value caller might want printed */

    vsnprintf(buf, MAXLINE, fmt, ap);

    if(errnoflag)

        snprintf(buf+strlen(buf), MAXLINE-strlen(buf), ": %s", strerror(errno_save));

    strcat(buf, "\n");

    if(log_to_stderr)

    {

        fflush(stdout);

        fputs(buf, stderr);    

        fflush(stderr);

    }

    else

    {

        syslog(priority, buf);

    }

}

本篇博文内容摘自《UNIX环境高级编程》（第二版），仅作个人学习记录所用。关于本书可参考：http://www.apuebook.com/。