C语言实现的linux下ls命令

用C语言实现linux下的ls -l命令。与文件相关的结构体、函数等等知识请看"stat结构体以及文件相关函数"

#include <stdio.h>#include <sys/types.h>#include <dirent.h>#include <sys/stat.h>#include <string.h>#include <unistd.h>#include <pwd.h>#include <grp.h> void do_ls(char *dirname);void dostat(char *filename);void show_file_info(char *filename, struct stat *info_p);void mode_to_letters(int mode, char * str);char *uid_to_name(uid_t uid);char *gid_to_name(gid_t gid); int main(int argc, char **argv){  if (argc == 1)  {     do_ls( "." );  }  else  {     while ( --argc )    {      printf("%s:\n", *++argv );      chdir(*argv); //切换到指定目录后再显示该目录的内容      do_ls( *argv );      chdir(""); //再回到当前工作目录来    }  }  return 0;} void do_ls( char * dirname ){  DIR    *dir_ptr;  struct dirent  *direntp;  /*  struct dirent  {    ino_t d_nio;    ff_t d_off;    signed short int d_reclen;    unsigned char d_type;    har d_name[256];    }  d_ino:目录进入点的inode  d_off:目录文件开头至此目录进入点的位移  d_reclen:d_name的长度，不包含NULL字符  d_type:d_ame所指文件类型  d_name:文件名  */  /*    opendir函数用来打开参数name指定的目录，    并返回DIR *形态的目录流  */  if ( ( dir_ptr = opendir( dirname ) ) == NULL )   {    fprintf(stderr,"ls1: cannot open %s, not a directory. treat as a file shown below:\n", dirname);    dostat( dirname ); //如果不是目录就当作文件来显示其属性  }  else  {    /*      readdir返回参数dir目录流的下个目录进入点    */    while ( ( direntp = readdir( dir_ptr ) ) != NULL )    {       dostat( direntp->d_name );/*逐个显示目录里文件信息*/    }    closedir(dir_ptr);  }} void dostat( char *filename ){  struct stat info;  if ( stat(filename, &info) == -1 )    /*取文件信息失败*/  {      perror( filename );  }  else          /*显示文件信息*/  {     show_file_info( filename, &info );  }} void show_file_info(char *filename, struct stat *info_p){  char modestr[11];   mode_to_letters(info_p->st_mode, modestr);   printf("%s"  , modestr);  //st_nlink连接该文件的硬链接数，刚建立的文件值为1  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, "----------");           /* default=无参数 */   if (S_ISDIR(mode))      str[0] = 'd';    /* 目录      */  if (S_ISCHR(mode))     str[0] = 'c';    /* 字符设备   */  if (S_ISBLK(mode))      str[0] = 'b';    /* 块设备     */   if (mode & S_IRUSR)     str[1] = 'r';    /* 用户权限  */  if (mode & S_IWUSR)     str[2] = 'w';  if (mode & S_IXUSR)     str[3] = 'x';   if (mode & S_IRGRP)     str[4] = 'r';    /* 组权限 */  if (mode & S_IWGRP)     str[5] = 'w';  if (mode & S_IXGRP)    str[6] = 'x';   if (mode & S_IROTH)     str[7] = 'r';    /* 其人的权限 */  if (mode & S_IWOTH)     str[8] = 'w';  if (mode & S_IXOTH)     str[9] = 'x';} char *uid_to_name(uid_t uid){  struct  passwd *pw_ptr;  static  char numstr[10];  //获取用户ID  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 *grp_ptr;  static  char numstr[10];  //获取组ID  if ((grp_ptr = getgrgid(gid)) == NULL)  {    sprintf(numstr,"%d", gid);    return numstr;  }  else  {     return grp_ptr->gr_name;  }}