How to add the data After reallocating a memory using a realloc() function?

Question

Consider I have a string called "bhuvanesh" , to store that string , Initially allocate the memory using malloc()

   char *ptr=(char *)malloc(sizeof("bhuvanesh"));
   sprintf(ptr,"bhuvanesh");

Then I want to add the string with the previously stored memory , the string is "waran". so I am using realloc()

 ptr=(char *)realloc(ptr,15);

The function realloc() will return the starting address, so concatenate the string I can use strcat() function

  strcat(ptr,"waran");

or else I can do like that

    char *p=ptr;
    p=p+sizeof("bhuvanesh");

    sprintf(p,"waran\n");

Is there is any way to do this ?

@RaymondChen - yes I want to know , any easiest way is available to do that? — Bhuvanesh, Jan 20 '15 at 13:55
@Bhuvanesh What do you imagine you'll find that is simpler than the strcat example you already gave? It's one function call that takes the two parameters that any other solution is also going to require. — Katie, Jan 20 '15 at 13:58

score 0 · Answer 1 · answered Aug 06 '15 at 06:51

This is correct:

  strcat(ptr,"waran");

This is faulty:

    char *p=ptr;
    p=p+sizeof("bhuvanesh");

    sprintf(p,"waran\n");

p=p+sizeof("bhuvanesh") results in p pointing after the string-terminating '\0'; correct would be

    p += sizeof"bhuvanesh" - 1;

or

    p += strlen(p);

Plus sprintf(p,"waran\n") adds 6 bytes to the string, but you have only reallocated 5 more, so either

 ptr = realloc(ptr, 16);

or dropping the '\n', e. g.

    strcpy(p, "waran");

would be appropriate.

score 0 · Answer 2 · answered Aug 06 '15 at 07:46

Leave the headache to the OS; not with you; I mean don't use strlen, strcpy and using + to find the exact locations; Now with this below approach you are done with what you want; Keep it simply stylish (KISS)

#include <stdio.h>
#include <malloc.h>
int main() 
{
    char *ptr = (char *) malloc(sizeof("bhuvanesh"));
    sprintf(ptr, "bhuvanesh");

    ptr = (char *)realloc(ptr, 15);

    sprintf(ptr, "%swaran", ptr);
    printf("%s\n", ptr);
    return 0;
}

How to add the data After reallocating a memory using a realloc() function?

2 Answers2