question regarding fopen - what am I doing wrong here? - c

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
static char *dup_str(const char *s)
{
size_t n = strlen(s) + 1;
char *t = (char*) malloc(n);
if (t)
{
memcpy(t, s, n);
}
return t;
}
static char **get_all_files(const char *path)
{
DIR *dir;
struct dirent *dp;
char **files;
size_t alloc, used;
if (!(dir = opendir(path)))
{
goto error;
}
used = 0;
alloc = 10;
if (!(files = (char**) malloc(alloc * sizeof *files)))
{
goto error_close;
}
while ((dp = readdir(dir)))
{
if (used + 1 >= alloc)
{
size_t new_thing = alloc / 2 * 3;
char **tmp = (char**) realloc(files, new_thing * sizeof *files);
if (!tmp)
{
goto error_free;
}
files = tmp;
alloc = new_thing;
}
if (!(files[used] = dup_str(dp->d_name)))
{
goto error_free;
}
++used;
}
files[used] = NULL;
closedir(dir);
return files;
error_free:
while (used--)
{
free(files[used]);
}
free(files);
error_close:
closedir(dir);
error:
return NULL;
}
int main(int argc, char **argv)
{
char **files;
size_t i;
if (argc != 2)
{
fprintf(stderr, "Usage: %s DIRECTORY\n", argv[0]);
return EXIT_FAILURE;
}
files = get_all_files(argv[1]);
if (!files)
{
fprintf(stderr, "%s: %s: something went wrong\n", argv[0], argv[1]);
return EXIT_FAILURE;
}
for (i = 0; files[i]; ++i)
{
FILE *fp;
if((fp = fopen(files[i],"r"))==NULL)
{
printf("error cannot open file\n");
exit(1);
}
fclose(fp);
}
for (i = 0; files[i]; ++i)
{
free(files[i]);
}
free(files);
return EXIT_SUCCESS;
}
I am just getting "error cannot open file".

Answer 1

If I invoke your program passing it /tmp as the argument.
files = get_all_files(argv[1]);
will return all the files in /tmp but when you do:
for (i = 0; files[i]; ++i) {
FILE *fp;
if((fp = fopen(files[i],"r"))==NULL)
you are trying to open those files from the present working directory. But they are present in the directory you passed as argument making your fopens fail.
To fix this
you prefix the dir name to the file
to be opened. or
You can change your pwd using chdir and then do the fopens.

Answer 2

A couple problems, I think:
readdir() returns subdirectories in the path, even entries like "." and "..".
you try to open the files returned, but in whatever the current directory might be - you need to concatenate the path to the filename you're opening.