how to iterate over files within a directory and compute a sha512 hash for each?

Question

This code below creates a hash of a file that is created, however I wondered where I should begin to convert this into a program that will scan a folder for files and automatically hash them? Tips, hints, and pointers on where to look to understand how to do this would be much appreciated!

#include <stdio.h>
#include <openssl/sha.h>

int main()
{
    unsigned char c[SHA512_DIGEST_LENGTH];
    char *filename="sha512.c";
    int i;
    FILE *inFile = fopen (filename, "rb");
    SHA512_CTX mdContext;
    int bytes;
    unsigned char data[1024];

    SHA512_Init (&mdContext);
    while ((bytes = fread (data, 1, 1024, inFile)) != 0)
        SHA512_Update (&mdContext, data, bytes);
    SHA512_Final (c,&mdContext);
    for(i = 0; i < SHA512_DIGEST_LENGTH; i++) printf("%02x", c[i]);
    printf (" %s\n", filename);
    fclose (inFile);
    return 0;
}

Understandably a loop is required, however I am unsure how to go about calculate each file only once (as opposed to continuously calculating files that have already been hashed). This code is utilising openssl.

Thank you in advance.

Are you asking how to iterate over files in a given directory? — Eugene Sh., Feb 28 '19 at 17:38
Yes, that's a much better description of what I would like to do - I'll edit the title in fact. — Wow Just wow, Feb 28 '19 at 17:42
Take a look here: https://stackoverflow.com/questions/1271064/how-do-i-loop-through-all-files-in-a-folder-using-c — Eugene Sh., Feb 28 '19 at 17:54

how to iterate over files within a directory and compute a sha512 hash for each?

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