C Filling a buffer - c

Question

I need to fill a buffer space with file descriptors of files from a defined source directory. So I have the startup code:
int main(int argc, char* argv[])
{
DIR *src=opendir(argv[1]);
struct dirent *DirEntry;
char* buffer[200];
do {
DirEntry = readdir(src);
if(DirEntry != NULL) {
//put file into buffer
}
}while(DirEntry!=NULL);
}
How do I complete this loop to place all file descriptors of a given directory into the array called 'buffer'? Should I use an object of DirEntry like DirEntry->d_name to return a file descriptor that I then put into the array?

Answer 1

If you need to move files from a source directory to a destination directory, you are going to need file names much more than you need file descriptors. With the names, you can open and close descriptors whenever needed; without the names, you can't create the files in the target directory sensibly. However, we can handle file descriptors too.
So, assuming you have strdup(), you might use:
typedef struct File
{
char *name;
int fd;
} File;
And in your loop:
if (DirEntry != NULL)
{
buffer[i].name = strdup(DirEntry->d_name);
if (buffer[i].name != 0)
buffer[i].fd = open(buffer[i].name, O_RDONLY);
i++;
}
where buffer is an array of File and i is a convenient integer:
enum { MAX_FILES = 4096 };
int i;
File buffer[MAX_FILES];
You should also add a condition to the main condition to ensure no overflow (or replace the fixed size buffer with a dynamically allocated one):
if (DirEntry != NULL && i < MAX_FILES)
You could sensibly break the loop if i reaches the limit. You could test whether the name represents a file (as opposed to FIFO, block device, character device, socket, symlink, directory, ...); you'd probably use stat() or lstat() for that. The file descriptor would be negative (-1) if the open() call failed. You might conserve entries by not incrementing i if the memory allocation fails, but it is probably not worth worrying about. If the memory allocation for a file name fails, there isn't going to be much else that works.

Answer 2

A file descriptor is "int" typed value that returned by open() system call. It's not in DirEntry structure. So, firstly, you should define the buffer array as int type, then you can open each file in the loop with open() system call, and save open() returned file descriptor in buffer array.

Answer 3

You question doesn't quite make sense. If you want file descriptors you have to open the file or directory with open() to get a file descriptor.
If you just want to store the names of the files in an array, then you can create a two dimensional array using malloc or calloc and copy the d_name member to the next available slot in the array. Alternatively you can use what you have and use a function such as strdup to copy the string to your array, but be careful because you'll need to free it later using free().
If you actually do want file descriptors, you will need to create an array of int rather than char *.