int str_printf(char** pdst, char* format, ...)
{
    va_list arg_ptr;

    va_start(arg_ptr, format);

    int x = vsprintf(*pdst, format, arg_ptr);

    va_end(arg_ptr);

    return (x);
}

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

    
void str_cpy (char **a,  const char *b) {  
   int _size = strlen(b)+1;

   *a =realloc(*a, _size);
   memmove(*a, b, _size);
}


void str_cat (char **a, const char *b){
   int _size1 = strlen(b);  

   *a =realloc(*a, _size1);
   memmove(*a + strlen(*a), b, _size1);
}

int main() {
   char *s = NULL;
  
   str_cpy(&s, "Hola Hola");    
   str_cpy(&s, s+5);    
   str_cat(&s," World");    
      
   return 0;
}

void str_cpy( char** to_str, char* from_str ) {
    if ( !from_str ) {
        return;
    }

      if ( !( *to_str = ( char* )realloc( *to_str, strlen(from_str)*sizeof(char) + sizeof(char) ) ) ) {
                return;
        }

    if ( !memmove( *to_str, from_str, strlen( from_str )*sizeof(char) + sizeof(char) ) ) {
        if ( !*to_str ) {
            free( *to_str );
        }
        *to_str=NULL;
    }
}

void str_cat(char** to_str, char* from_str) {

    if ( !from_str ) {
        return;
    }

      if ( !( *to_str = ( char* )realloc( *to_str, ( !*to_str ? 0: strlen(*to_str)*sizeof(char) ) + strlen(from_str)*sizeof(char) + sizeof(char) ) ) ) {
                return;
        }

    if ( !memmove( *to_str + ( !*to_str ? 0: strlen(*to_str)*sizeof(char) ), from_str, strlen( from_str )*sizeof(char) + sizeof(char) ) ) {
        if ( !*to_str ) {
            free( *to_str );
        }
        *to_str=NULL;
    }

    
}

Thank you for taking the time to answer our challenge.

Unfortunately the answer you gave is not the answer we are looking for. I do hope that you at least enjoyed the challenge (-;

In all solutions that don't pass this stage we find at least 2 problems from the list of blocking problems that you can find at http://www.hola.org/issues.html

We realize that the bugs in your solution may have been due to a  hasty submission. Therefore, if this was your 1st submission you  are welcome re-check your code carefully, use the issues list we  gave, and try a 2nd attempt.

You can send this challenge to programmers you know and if they   will answer  the
question perfectly then you and your friend may win 2K NIS...Please remember to CC me when you forward the link to the challenge so I will know they came from you (http://www.TheCodeIL.com/5min_forward_rules.html).

Below is an email that you can use to forward to your friends.

Good Luck and again, Thank you!

strlen(from_str)*sizeof(char)