Question

Hi I am getting the the following error from valgrind.

Conditional move based on uninitialized values, Uninitalized values was created by heap allocation.

The compiler does not complain.

I looked at most of the similar errors at stackoverflow, but I can’t seem to pinpoint what’s wrong with mine.

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

    int
    main(void)
     {

      char *string1 = malloc(45);
      char string2[25] = "HELLO WORLD";
      strcpy(string1,string2);
      printf("String one is %s\n",string1);

      char string3[25];
      for (int i = 0; i < 25; i++)
       {
        string3[i] = tolower(string1[i]);

       }
      printf("The output is %s\n",string3);
      free(string1);
      return 0;

    }

Answer 1

You’re looping from 0 to 24 along string1, which has only been initialized strlen("HELLO WORLD") + 1 bytes. Bytes indexed from 12 to 24 there have not been initialized, and you shouldn’t be trying to read them. You should either use calloc() to allocate string1 or use memset() to initialize it, like so:

char *string1 = calloc(1, 45);

or

char *string1 = malloc(45);
memset(string1, 0, 45);

Or you could initialize string3 to zeroes with the above methods and then only copy strlen(string1) bytes.