Does realloc free fairly?

Applications Programming
1

Hello,
my program works properly but valgrind tells me I am not freeing allocated memory. I think the problem is in realloc.
I am pretty sure I do something wrong with realloc, because I changed it a bit and valgrind noticed less errors (that the program wasn't working properly with less errors is another question).
Thank you very much!
My example:

char *str1;
str1 = malloc(15 * sizeof(char));

for (x;y;z){
  //in this place I need to have str everytime clear - maybe new allocated
  //realloc works properly, but memory (?)

  str1 = realloc(NULL, 15 * sizeof(char));
  
  str1 = <any data>;
  
  processIt(str1); //processIt as a void func
}
free(str1);
2

You can refer the manual page of realloc. it should be like this:

str1 = realloc(str1, 15 * sizeof(char));

in such case, realloc will free the memory allocated before if need.

when the first parameter is NULL, its function is the same with malloc, of course there is memory leak.

3

Replace all instances of malloc and realloc with calloc. This way the memory is cleared that is reset to all 0's before starting fresh.

4

"str1=<any data>;" is leaking memory. That should be something like strncpy, memcpy or the likes