CODEWITHSUNDEEP
cpointerspointer-arithmetic
Shikha-SeniorDeveloper
Shikha-SeniorDeveloper

Reputation: 35

Printing entered string using pointer manipulation

I am new to pointers, please let me know how can i print the entered character.

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

   int main()
   {
      char *ptr;
      ptr = malloc(32 * sizeof(char));
      *ptr = 'h';
      ptr++;
      *ptr = 'e';
      ptr++; 
      *ptr = 'l';
      ptr++;
      *ptr = 'l';
      ptr++;
      *ptr = 'o';
      ptr++;
      *ptr = '\n';

      printf("value entered is %s\n", ptr);

      return 0;
    }

I want to print hello

Upvotes: 2

Views: 61

Answers (3)

cocool97
cocool97

Reputation: 1251

You can, rather using the malloc() function, use the calloc() function, which achieves the same goal of malloc(), but fills the memory with '\0'. This makes it easier to play with non-fixed length strings.
You can find the documentation of this function here.

Here is the code I've made : 

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

int main()
{
  char *ptr;
  ptr = calloc(32,sizeof(char));
  *ptr = 'h';
  ptr++;
  *ptr = 'e';
  ptr++; 
  *ptr = 'l';
  ptr++;
  *ptr = 'l';
  ptr++;
  *ptr = 'o';
  ptr++;
  *ptr = '\0';  //It should be null terminated

  ptr -= 5;
  printf("value entered is %s\n", ptr);

  free(ptr);

  return 0;
}

Upvotes: 0

Lundin
Lundin

Reputation: 213842

You should fix your code like this, with a temporary pointer:

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

int main (void)
{
  char* ptr;
  ptr = malloc(32 * sizeof(char));
  if(ptr == NULL)
  {
    puts("Allocation failed");
    return EXIT_FAILURE;
  }

  char* tmp = ptr;

  *tmp = 'h';
  tmp++;
  *tmp = 'e';
  tmp++; 
  *tmp = 'l';
  tmp++;
  *tmp = 'l';
  tmp++;
  *tmp = 'o';
  tmp++;
  *tmp = '\0'; // NOTE: null termination not \n

  printf("value entered is %s\n", ptr);
  free(ptr);    

  return 0;
}

A proper version without messy pointer arithmetic looks like this:

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

int main (void)
{
  char* ptr;
  ptr = malloc(32 * sizeof(char));
  if(ptr == NULL)
  {
    puts("Allocation failed");
    return EXIT_FAILURE;
  }

  strcpy(ptr, "hello");
  printf("value entered is %s\n", ptr);
  free(ptr);

  return 0;
}

Upvotes: 4

Blaze
Blaze

Reputation: 16876

You forgot the null-terminator. Add this:

ptr++;
*ptr = '\0';

Also, the pointer is now pointing to the null-terminator (or previously the newline character). You have to set it back to point to the 'h' again:

ptr -= 6;

And when you're done, you should free the memory:

free(ptr);

Upvotes: 5

Related Questions