C - Valgrind and "Conditional jump or move depends on uninitialised value(s)" error

Question

I have a problem with OPT algorithm as valgrind is giving me error (Conditional jump or move depends on uninitialised value(s)) at line #87. I guess it has something to do with "break", is there a way to fix this?

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

int convert_one_char(const char c) {
  if( c == '0' ) return 0;
  else if( c == '1' ) return 1;
  else if( c == '2' ) return 2;
  else if( c == '3' ) return 3;
  else if( c == '4' ) return 4;
  else if( c == '5' ) return 5;
  else if( c == '6' ) return 6;
  else if( c == '7' ) return 7;
  else if( c == '8' ) return 8;
  else if( c == '9' ) return 9;
  else return -1;
}

void print(int n[], int size) {
  int i;
  for (i = 0; i < size; i++) {
    printf("%d", n[i]);
    if (i != size-1) {
      printf(" | ");
    } else {
      printf(": ");
    }
  }
}

int main (int argc, char *argv[]) {
  /* argc should be 3 */
  if (argc != 3) {
    printf("Napaka: Potrebna sta 2 argumenta!\n");
  } else  {
    FILE *file = freopen(argv[2], "r", stdin);
    if (file == 0) {
      printf( "Napaka: 404!\n" );
    } else {
      int num_count = 0, len = atoi(argv[1]), buff[80], i = 0;
      char c;

      /* read file contents */
      do {
        c = getchar();
        if (i%2 == 0 && isdigit(c)) {
          buff[num_count] = convert_one_char(c);
          num_count++;
        }
        i++;
      } while (c != EOF);

      /* print parsed file */
      printf("Referencni niz: ");
      for (i = 0; i < num_count; i++) printf("%d ", buff[i]);

      printf("\n");

      /* opt algorithm */

      int frameset[len];
      int flag[len];
      for (i = 0; i < len; i++) { 
        frameset[i] = -1;
        flag[i] = 0;
      }

      int j, s, k, tmp, available = 1, max = 0, pos, pf = 0;

      for (i = 0; i < len; i++) {
        frameset[i] = buff[i];
        print(frameset, len);
        printf("Vstavim %d\n", buff[i]);
        pf++;
      }

      while (i < num_count) {
        max = 0;
        for (k = 0; k < len; k++) if (frameset[k] == buff[i]) available = 0;

        if(available == 1) {
          for(j = 0; j < len; j++) {

            for(s = i+1; s >= 0; s++) {
              if(frameset[j] == buff[s]) {
                flag[j] = s; // <<< line 87
                break;
              }

              if(s >= num_count) {
                flag[j] = 100;
                break;
              }
            }
          }
          for(k = 0; k < len; k++) {
            if (flag[k] > max) {
              max = flag[k];
              pos = k;
            }
          }


          frameset[pos] = buff[i];
          print(frameset, len);
          printf("Vstavim %d\n", buff[i]);

          pf++;
        } else {
          i++;
          available = 1;
        }
      }        

      printf("\n\nStevilo napak: %d\n", pf);
      fclose( file );
    }
  }
}

Answer 1

The for loop at line 85 looks strange. You are incrementing s, and continuing as long as it stays greater than 0. But i doesn't look negative to me, so s would always be greater than 0. Also, i doesn't look correctly initialized, as it is just set to len after the loop at line 71. Is that by design?

Basically, it looks as though you are comparing with buff[s], but you are incrementing s more than what you may have done when initializing buff.

Answer 2

I think you have to initialize all your variables, as "int j, s, k, tmp, available = 1, max = 0, pos, pf = 0;" because you are using all those variables inside conditionals..

EDIT: it is also a good practice...

Answer 3

Seems like you need to initialize all elements of your buff[80] and frameset[len] to something.. maybe 0

Also you also need to ensure that len is not greater than 80 otherwise you will be reading outside of an array.

if(frameset[j] == buff[s]) {
                flag[j] = s;
                break;
              }