Thread: Need help with Multithreading & Pointers in C

Okay so ill try my best at explaining this problem as I struggle with pointers.

I have an assignment for university in which I have to alter a pre-made password cracking program and make it multi threaded but just cant seem to get my head around the problem i'm having. i will try and post only the necessary information

So i have 4 pre created encrypted passwords stored within the array 'encrypted_passwords' and i need to use the multi-threading to be able to crack them much faster.

I have then created a struct that contains that starting value for each thread and the stride for each so that they do not overlap, also i have the pointer to the passwords 'salt_and_encrypted' that is declared at the start.

I then (in the main) create the threads and also set the values for the arguments for each thread before starting the threads running on the 'crack' method.

Edit: Errors - CrackMT.c:126:30: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types] t1_args.salt_and_encrypted = encrypted_passwords;
The errors are related to each of the t1_args, t2_args, t3_args and t4_args where i attempt to set the salt_and_encrypted to encrypted_password.

Code:

char * salt_and_encrypted;
char *encrypted_passwords[] = { 
"$6$KB$./CyqoGai/YYFHYBAT.tSdTuYEqW/XY2Y53D7xV/rU6QtJBThh1i3zffnptK6pJTUgMiZnV6fwjyyFMckLJuP.",
"$6$KB$sig9RP1foJmxO9Q/bzDukmLxWluzHxs5xGyNbQVdrFf.mc4jhztG6eV37qRKU/SHyuFvOh2H.bz8a3oEOkDLS.",
"$6$KB$5f63QAb4.5CLFgeTNRuRBQwLgyAxEefgjvIRqzhJqP9SGGTfCuP0ZuGhuxzivK6Z8Ywod4XaMIjXl8Sxi99iv1",
"$6$KB$CNwwbZPmnN53QUM0l19W9gkCsgUGWFPZntW9u94Oso4j0zHl6mQsPrNuOvFH4tSJiP4fo/MMq08lTeVXRtgGh1"
};


typedef struct arguments_t {
  int start;
  int stride;
  char *salt_and_encrypted;
} arguments_t;

void *crack(void *be){

arguments_t *args = (arguments_t *) be; 
printf("%c",'A');

  int w, x, y, z;    // Loop counters (added W for extra loop below)
  char salt[8];    // String used in hashing the password. Need space for \0
  char plain[8];   // The combination of letters currently being checked
  char *enc;       // Pointer to the encrypted password
  int count = 0;   // The number of combinations explored so far

  substr(salt, salt_and_encrypted, 0, 7);
    for(w=args->start; w<='Z'; w+=args->stride){
      for(x='A'; x<='Z'; x++){
        for(y='A'; y<='Z'; y++){
          for(z=0; z<=99; z++){
        sprintf(plain, "%c%c%c%02d", w, x, y, z);
        enc = (char *) crypt(plain, salt);
        count++;
        if(strcmp(salt_and_encrypted, enc) == 0)
        {
          //printf("#%-8d%s %s\n", count, plain, enc);
        } 
        else 
        {
          //printf(" %-8d%s %s\n", count, plain, enc);
        }
          }
        }
      }
    }
  printf("%d solutions explored\n", count);
}

int main(int argc, char *argv[]){

//define 4 threads
pthread_t t1, t2, t3, t4;

//set argruments for each thread
  arguments_t t1_args;
  t1_args.salt_and_encrypted = encrypted_passwords;
  t1_args.start = 0;
  t1_args.stride = 4;

  arguments_t t2_args;
  t2_args.salt_and_encrypted = encrypted_passwords;
  t2_args.start = 1;
  t2_args.stride = 4;

  arguments_t t3_args;
  t3_args.salt_and_encrypted = encrypted_passwords;  
  t3_args.start = 2;
  t3_args.stride = 4;

  arguments_t t4_args;
  t4_args.salt_and_encrypted = encrypted_passwords;
  t4_args.start = 3;
  t4_args.stride = 4;

  void *crack();

  //create each thread
  pthread_create(&t1, NULL, crack, &t1_args);
  pthread_create(&t2, NULL, crack, &t2_args);
  pthread_create(&t3, NULL, crack, &t3_args);
  pthread_create(&t4, NULL, crack, &t4_args);

  //join the threads to end 
  pthread_join(t1, NULL);
  pthread_join(t2, NULL);
  pthread_join(t3, NULL);
  pthread_join(t4, NULL);
}

Any help will be appreciated as the course material that was covered was not useful at all. If i have missed anything from the code that would make it easier for you to help me I will add later if needed.

> t1_args.salt_and_encrypted = encrypted_passwords;
The RHS is an array, so you need to say something like
t1_args.salt_and_encrypted = encrypted_passwords[0];

The prototype on line 76 (as posted) is useless.

> substr(salt, salt_and_encrypted, 0, 7);
salt_and_encrypted is the uninitialised global, not the parameter you pass with the same name.

> char *encrypted_passwords[]
TBH, you have 4 of these, and 4 threads.
The .start and .stride seem to be red herrings.