Linux C变成小例子——实现ls命令

/*
* ls2.c
*
*  Created on: Dec 30, 2013
*      Author: fedora
*/
#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.h>
#include <pwd.h>
#include <grp.h>

void show_file_info(char* filename, struct stat* info_p) {
char* uid_to_name(), *ctime(), *gid_to_name(), *filemode();
void mode_to_letters();
char modestr[11];

mode_to_letters(info_p->st_mode, modestr);

printf("%s", modestr);
printf(" %4d", (int) info_p->st_nlink);
printf(" %-8s", uid_to_name(info_p->st_uid));
printf(" %-8s", gid_to_name(info_p->st_gid));
printf(" %8ld", (long) info_p->st_size);
printf(" %.12s", 4 + ctime(&info_p->st_mtime));
printf(" %s\n", filename);

}

void mode_to_letters(int mode, char str[]) {
strcpy(str, "----------");

if (S_ISDIR(mode)) {
str[0] = 'd';
}

if (S_ISCHR(mode)) {
str[0] = 'c';
}

if (S_ISBLK(mode)) {
str[0] = 'b';
}

if ((mode & S_IRUSR)) {
str[1] = 'r';
}

if ((mode & S_IWUSR)) {
str[2] = 'w';
}

if ((mode & S_IXUSR)) {
str[3] = 'x';
}

if ((mode & S_IRGRP)) {
str[4] = 'r';
}

if ((mode & S_IWGRP)) {
str[5] = 'w';
}

if ((mode & S_IXGRP)) {
str[6] = 'x';
}

if ((mode & S_IROTH)) {
str[7] = 'r';
}

if ((mode & S_IWOTH)) {
str[8] = 'w';
}

if ((mode & S_IXOTH)) {
str[9] = 'x';
}
}

char* uid_to_name(uid_t uid){
struct passwd* getpwuid(),* pw_ptr;
static char numstr[10];

if((pw_ptr = getpwuid(uid)) == NULL){
sprintf(numstr,"%d",uid);

return numstr;
}else{
return pw_ptr->pw_name;
}
}

char* gid_to_name(gid_t gid){
struct group* getgrgid(),* grp_ptr;
static char numstr[10];

if(( grp_ptr = getgrgid(gid)) == NULL){
sprintf(numstr,"%d",gid);
return numstr;
}else{
return grp_ptr->gr_name;
}
}
void do_ls(char dirname[]) {
DIR* dir_ptr;
struct dirent* direntp;

if ((dir_ptr = opendir(dirname)) == NULL) {
fprintf(stderr, "ls2: cannot open %s \n", dirname);
} else {
while ((direntp = readdir(dir_ptr)) != NULL) {
dostat(direntp->d_name);
}

close(dir_ptr);
}
}

void dostat(char* filename) {
struct stat info;

if (stat(filename, &info) == -1) {
perror(filename);
} else {
show_file_info(filename, &info);
}
}

int main(int ac,char* av[]){
if(ac == 1){
do_ls(".");
}else{
while(--ac){
printf("%s: \n",*++av);
do_ls(*av);
}
}
}