如果知道一個用戶的用戶ID或者登錄名,可以通過getpwuid或getpwnam函數獲得用戶的登錄信息.
函數原型為:
       #include <pwd.h>
       #include <sys/types.h>

       struct passwd *getpwnam(const char *name);
       struct passwd *getpwuid(uid_t uid);

 The passwd structure is defined in <pwd.h> as follows:

              struct passwd {
                      char    *pw_name;       /* user name */
                      char    *pw_passwd;     /* user password */
                      uid_t   pw_uid;         /* user id */
                      gid_t   pw_gid;         /* group id */
                      char    *pw_gecos;      /* real name */
                      char    *pw_dir;        /* home directory */
                      char    *pw_shell;      /* shell program */
              };

使用舉例:
#include <pwd.h>
#include <sys/types.h>
#include <stdio.h>

main()
{
    uid_t my_uid;
    my_uid = 500;

    struct passwd *my_info;

    my_info = getpwuid( my_uid );
    //my_info = getpwnam( "fflg" );

    printf( "my name     = [%s]\n", my_info->pw_name     );
    printf( "my passwd = [%s]\n", my_info->pw_passwd );
    printf( "my uid          = [%d]\n", my_info->pw_uid          );
    printf( "my gid          = [%d]\n", my_info->pw_gid          );
    printf( "my gecos    = [%s]\n", my_info->pw_gecos     );
    printf( "my dir           = [%s]\n", my_info->pw_dir           );
    printf( "my shell       = [%s]\n", my_info->pw_shell       );
}
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