stat()失败:没有这样的文件或目录

我想获得具有权限等文件和文件夹的列表，但对于每个项目，我得到stat错误"没有这样的文件或目录"和列表只包含项目"."answers".. "

list<string> res;
DIR *dirp;
dirp = opendir("/");
struct dirent *dp;
while ((dp = readdir(dirp)) != NULL){
    stringstream ss;
    struct stat fileStat;
    if(stat(dp->d_name, &fileStat) < 0)    {
        std::cout << "stat() failed: " << std::strerror(errno) << "(" << dp->d_name << ")" << endl;
        continue;
    }

    ss << ( (S_ISDIR(fileStat.st_mode)) ? "d" : "-" )
     << ( (fileStat.st_mode & S_IRUSR) ? "r" : "-")
     << ((fileStat.st_mode & S_IWUSR) ? "w" : "-")
     << ((fileStat.st_mode & S_IXUSR) ? "x" : "-")
     << ((fileStat.st_mode & S_IRGRP) ? "r" : "-")
     << ((fileStat.st_mode & S_IWGRP) ? "w" : "-")
     << ((fileStat.st_mode & S_IXGRP) ? "x" : "-")
     << ((fileStat.st_mode & S_IROTH) ? "r" : "-")
     << ((fileStat.st_mode & S_IWOTH) ? "w" : "-")
     << ((fileStat.st_mode & S_IXOTH) ? "x" : "-") << "t"
     << fileStat.st_nlink << "t"
     << fileStat.st_uid << "t"
     << fileStat.st_gid << "t"
     << fileStat.st_size << "t";
    char mbstr[100];
    time_t t = (time_t)fileStat.st_mtim.tv_sec;        
    struct tm *tminfo = localtime ( &t );
    strftime(mbstr, sizeof(mbstr), "%b %d %H:%M", tminfo  );
    ss << mbstr << "t"
       << dp->d_name;
    res.push_back(ss.str());
}
for( string s : res ){
    cout << s << endl;
}

...
stat() failed: No such file or directory(usr)
stat() failed: No such file or directory(var)
stat() failed: No such file or directory(home)
stat() failed: No such file or directory(etc)
stat() failed: No such file or directory(bin)
drwxrwxr-x      9       1000    1000    4096    May 29 02:08    .
drwxrwxr-x      3       1000    1000    4096    Mar 16 22:36    ..

上面的例子是根目录"/"，我已经尝试了很多目录，但只有当前目录"."没有出现错误。