Heap memory in c-CodePudding

Can you resize a array in C without losing the data of the array with the previous size?

malloc() puts your data in heap memory but every time you call malloc() it chooses as a starting position a different position in heap memory

CodePudding user response：

In the general case, that is not always possible, as there maybe no room to expand at that memory location. There is a CRT function called realloc which either expands in-place, or allocates new buffer and moves all your data there. Here's how you use it:

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

int main() {
  void* p = malloc(10);
  if (!p) {
    puts("Failed to allocate 10 bytes.");
    return 0;
  }

  puts("Allocated 10 bytes");

  void* tmp = realloc(p, 15);

  if (!tmp) {
    puts("Failed to allocate more memory");
    free(p); // if allocation fails, you need to free the old buffer
    return 0;
  }

  puts("Allocated 15 bytes");

  if (tmp == p) {
    puts("Start pointer still same");
  }

  // if allocation succeeds with realloc, 
  // you only need to free the new buffer 
  // even if expansion was not in-place.
  free(tmp); 
}

See the documentation.