Implementing the ls -al command in C

Question

As a part of an assignment from one of my classes, I have to write a program in C to duplicate the results of the ls -al command. I have read up on the necessary materials but I am still not getting the right output. Here is my code so far, its only supposed to print out the file size and the file name, but the file sizes its printing are not correct.

Code:

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

int main(int argc, char* argv[])
{
    DIR *mydir;
    struct dirent *myfile;
    struct stat mystat;

    mydir = opendir(argv[1]);
    while((myfile = readdir(mydir)) != NULL)
    {
        stat(myfile->d_name, &mystat);    
        printf("%d",mystat.st_size);
        printf(" %s\n", myfile->d_name);
    }
    closedir(mydir);
}

These are my results after executing the code:

[root@localhost ~]# ./a.out Downloads
4096 ..
4096 hw22.c
4096 ankur.txt
4096 .
4096 destination.txt

Here are the correct sizes:

[root@localhost ~]# ls -al Downloads
total 20
drwxr-xr-x.  2 root root 4096 Nov 26 01:35 .
dr-xr-x---. 24 root root 4096 Nov 26 01:29 ..
-rw-r--r--.  1 root root   27 Nov 21 06:32 ankur.txt
-rw-r--r--.  1 root root   38 Nov 21 06:50 destination.txt
-rw-r--r--.  1 root root 1139 Nov 25 23:38 hw22.c

Can anyone please point out my mistake.

Thanks,

Ankur

Answer 1

myfile->d_name is the file name not the path, so you need to append the file name to the directory "Downloads/file.txt" first, if it's is not the working directory:

char buf[512];    
while((myfile = readdir(mydir)) != NULL)
{
    sprintf(buf, "%s/%s", argv[1], myfile->d_name);
    stat(buf, &mystat);
....

As to why it prints 4096 that is the size of the links . and .. from the last call to stat().

Note: you should allocate a buffer large enough to hold the directory name, the file name the NULL byte and the separator, something like this

strlen(argv[1]) + NAME_MAX + 2;

Answer 2

This is the final code I got to work for anyone interested. It prints the correct file sizes. Credit goes to asker and mux for answering, just putting the code together. Input I got this to work for is "./main ." .

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

int main(int argc, char* argv[])
{
    DIR *mydir;
    struct dirent *myfile;
    struct stat mystat;

    char buf[512];
    mydir = opendir(argv[1]);
    while((myfile = readdir(mydir)) != NULL)
    {
        sprintf(buf, "%s/%s", argv[1], myfile->d_name);
        stat(buf, &mystat);
        printf("%zu",mystat.st_size);
        printf(" %s\n", myfile->d_name);
    }
    closedir(mydir);
}