linux 下用 c 实现 ls -l 命令

#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.h>
#include <string.h> 

void do_ls(char[]);
void dostat(char *);
void show_file_info( char *, struct stat *);
void mode_to_letters( int , char[] );
char * uid_to_name( uid_t );
char * gid_to_name( gid_t ); 

main(int ac, char *av[])
{
    if( ac ==  )
    do_ls( "." );          /*显示当前目录*/
    else
    while( --ac ){
        printf("%s:\n", *++av);   /*显示参数指定的目录*/
        do_ls( *av );
    }
} 

void do_ls( char dirname[] )
{
    DIR *dir_ptr;
    struct dirent *direntp; 

    if( (dir_ptr = opendir( dirname )) == NULL)            /*打开目录,成功则返回 DIR 结构指针*/
    fprintf(stderr, "ls1: cannot open %s\n", dirname); 

    else
    {
    while( ( direntp = readdir( dir_ptr ) ) != NULL )
         dostat( direntp->d_name ); 

    closedir( dir_ptr );
    }
} 

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

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

void show_file_info( char *filename, struct stat *info_p )
{ 

   if(filename[]!='.')
   {
    char *uid_to_name(), *ctime(), *gid_to_name(), *filemode();
    void mode_to_letters(); 

    char modestr[]; 

    mode_to_letters( info_p->st_mode, modestr );      /*模式到字符的转换*/ 

    printf("%s", modestr );                           /*输出模式标识符*/ 

    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 ",  + ctime(&info_p->st_mtime)); 

    printf("%s\n",filename);
   }    

} 

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

    if( S_ISDIR(mode) ) str[] = 'd';                 /*目录*/
    if( S_ISCHR(mode) ) str[] = 'c';                 /*字符文件*/
    if( S_ISBLK(mode) ) str[] = 'b';                 /*块文件*/ 

    if(mode & S_IRUSR)  str[] = 'r';
    if(mode & S_IWUSR)  str[] = 'w';
    if(mode & S_IXUSR)  str[] = 'x'; 

    if(mode & S_IRGRP)  str[] = 'r';
    if(mode & S_IWGRP)  str[] = 'w';
    if(mode & S_IXGRP)  str[] = 'x'; 

    if(mode & S_IXOTH)  str[] = 'r';
    if(mode & S_IXOTH)  str[] = 'w';
    if(mode & S_IXOTH)  str[] = 'x';
} 

#include <pwd.h> 

    char *uid_to_name( uid_t uid )
/*
*返回和 uid 相应的用户名的指针
*/
    {
    struct passwd *getpwuid(), *pw_ptr;
    static char numstr[]; 

    if( ( pw_ptr = getpwuid( uid ) ) == NULL ) {
        sprintf(numstr, "%d", uid);      /*没有对应的用户名则 uid 存入 numstr,返回后以字符串的形式打印 uid*/
        return numstr;
    }
    else
        return pw_ptr->pw_name;          /*打印用户名*/
    } 

#include <grp.h> 

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

    if( ( grp_ptr = getgrgid(gid) ) == NULL ){ 

        sprintf(numstr, "%d", gid);
        return numstr;
    }
    else
        return grp_ptr->gr_name;
    }