APUE_1UNIXSystemOverview Figure1.3ListAllTheFilesInADirectory

// 1.3ListAllTheFilesInADirectory.cpp
#include <dirent.h>

#include "../apuesunyj.h"

int main(int argc, char *argv[])
{
	DIR* dp;
	struct dirent* dirp;
	if (2 != argc)
	{
		err_quit("usage: ls directory_name");
	}
	if ((dp = opendir(argv[1])) == NULL)
	{
		err_sys("can’t open %s", argv[1]);
	}
	while ((dirp = readdir(dp)) != NULL)
	{
		printf("%s
", dirp->d_name);
	}
	closedir(dp);
	return 0;
}

// error.cpp
#include "apuesunyj.h"

int64_t const MAXLINE = 4096; // max line length
/*
 *  * Print a message and return to caller.
 *   * Caller specifies "errnoflag".
 *    */
static void err_doit(int errnoflag, int error, const char *fmt, va_list ap)
{
    char buf[MAXLINE];

    vsnprintf(buf, MAXLINE, fmt, ap);
    if (errnoflag)
        snprintf(buf + strlen(buf), MAXLINE - strlen(buf), ": %s", strerror(
                    error));
    strcat(buf, "
");
    fflush(stdout);/* in case stdout and stderr are the same */
    fputs(buf, stderr);
    fflush(NULL);/* flushes all stdio output streams */
}

/*
 *  * Fatal error unrelated to a system call.
 *   * Print a message and terminate.
 *    */
void err_quit(const char *fmt, ...)
{
    va_list ap;

    va_start(ap, fmt);
    err_doit(0, 0, fmt, ap);
    va_end(ap);
    exit(1) ; // process terminate, not just like return, totally different
}

/*
 *  * Fatal error related to a system call.
 *   * Print a message and terminate.
 *    */
void err_sys(const char *fmt, ...)
{
    va_list ap;

    va_start(ap, fmt);
    err_doit(1, errno, fmt, ap);
    va_end(ap);
    exit(1) ;
}

// apuesunyj.h
#ifndef APUE_SUNYJ
#define APUE_SUNYJ

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>

void err_quit(const char *fmt, ...);
void err_sys(const char *fmt, ...);


#endif