Reading all files in two directories at the same time - c

Question

I have a problem with task. I have two path to directories. I can read all files from first path in argv[1] but can't open files from second folder from argv[2]. Quantity of files is equal. The way at the begining to write name of fales in array is failed because their is about a few hundred.I have an example how I try reading files. Need help. Thanks!
#include "stdafx.h"
#include "windows.h"
int main(int argc, char* argv[])
{
FILE *fp = 0;
uchar tmpl1[BUFFER_SIZE] = { 0 };
uchar tmpl2[BUFFER_SIZE] = { 0 };
size_t size;
size_t n;
FILE *Fl = 0;
if (argc != 3 || argv[1] == NULL || argv[2] == NULL)
{
printf("Error", argv[0]);
return -1;
}
char Fn[255];
HANDLE hFind;
WIN32_FIND_DATA ff;
char Fn1[255];
HANDLE hFind1;
WIN32_FIND_DATA ff1;
sprintf_s(Fn, 255, "%s\\*", argv[1]);
sprintf_s(Fn1, 255, "%s\\*", argv[2]);
if ((hFind = FindFirstFile(Fn, &ff)) != INVALID_HANDLE_VALUE)
{
if ((hFind1 = FindFirstFile(Fn1, &ff1)) != INVALID_HANDLE_VALUE)
{
do
{
if (ff.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) continue;
ff1.dwFileAttributes;
sprintf_s(Fn, "%s\\%s", argv[1], ff.cFileName);
sprintf_s(Fn1, "%s\\%s", argv[2], ff1.cFileName);
// here I can't read file's name from second folder
printf(Fn, "%s\\%s", argv[1], ff.cFileName);
printf(Fn1, "%s\\%s", argv[2], ff1.cFileName);
if (fopen_s(&fp, Fn, "rb") != 0)
{
printf("Error reading\nUsage: %s <tmpl1>\n", argv[1]);
return -1;
}
size = _filelength(_fileno(fp));
n = fread(tmpl1, size, 1, fp);
fclose(fp);
fp = 0;
} while (FindNextFile(hFind, &ff));
// also I have a problem how read next file in second directory
FindClose(hFind);
}
}
return 0;
}

Answer 1

I didn't read why you want to scan two directories concurrently.
When I saw "at the same time" in the title I thought "concurrently". Afterwards, I saw the presented code and realized it shall be done rather "interleaved" instead of "concurrently" but that's not essential.
I assume you want to associate the file names in the first directory somehow to the file names in the second directory. This might be comparing the file names, read data from a file of first directory and read other data from an associated file of second directory, or may be something completely different.
However, based on this assumption, you have to consider that:
You should not assume to get file names in any useful order when scanning with FindFirstFile()/FindNextFile(). These functions return the files in its "physical order" i.e. how they are listed internally. (At best, you get . and .. always as first entries but I even wouldn't count on this.)
Considering this, I would recommend the following procedure:
read file names from first directory and store them in an array names1
read file names from second directory and store them in an array names2
sort arrays names1 and names2 with an appropriate criterion (e.g. lexicographically)
process the arrays names1 and names2.
As you see, the "read file names from directory and store them in an array" could be implemented as function and re-used as well as the sorting.
This said, finally, the answer for how to interleave two directory scans:
HANDLE hFind1 = FindFirstFile(Fn1, &ff1);
HANDLE hFind2 = FindFirstFile(Fn2, &ff2);
while (hFind1 != INVALID_HANDLE_VALUE || hFind2 != INVALID_HANDLE_VALUE) {
if (hFind1 != INVALID_HANDLE_VALUE) {
/** #todo process ff1 somehow */
}
if (hFind2 != INVALID_HANDLE_VALUE) {
/** #todo process ff2 somehow */
}
/* iterate: */
if (!FindNextFile(hFind1, &ff1)) {
FindClose(hFind1); hFind1 = INVALID_HANDLE_VALUE;
}
if (!FindNextFile(hFind2, &ff2)) {
FindClose(hFind2); hFind2 = INVALID_HANDLE_VALUE;
}
}
Please, note that I "abuse" the handles hFind1 and hFind2 itself for loop repetition. Thus, I do not need the extra ifs. (I like things like that.)
Btw. this loop iterates until both directories are scanned completely (even if they don't contain the same number of entries).
If you want to iterate instead until at least one directory is scanned completely you may achieve this by simply changing the while condition to:
while (hFind1 != INVALID_HANDLE_VALUE && hFind2 != INVALID_HANDLE_VALUE) {
if the loop shall be terminated as soon as at least one directory scan fails.
At last, a little story out of my own past (where I learnt a useful lesson regarding this):
I just had finished my study (of computer science) and was working at home on a rather fresh installed Windows NT when I started to copy a large directory from a CD drive to harddisk. The estimated time was round-about 1 hour and I thought: 'Hey. It does multi-tasking!' Thus, I started a second File Manager to copy another directory from this CD drive concurrently. When I hit the OK button, the prompt noises of the CD drive alerted me as well as the estimated time which "exploded" to multiple hours. After that, I behaved like to expect: tapped on my forehead and mumbled something like "unshareable resources"... (and, of course, stopped the second copying and went for a coffee instead.)