Implementation of Realloc in C
c, free, malloc, realloc
Solution
There is no portable way to get the size of memory allocated by malloc().
However, one can always do something like that to simulate what you want.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void myfree(void * p) {
size_t * in = p;
if (in) {
--in; free(in);
}
}
void * mymalloc(size_t n) {
size_t * result = malloc(n + sizeof(size_t));
if (result) { *result = n; ++result; memset(result,0,n); }
return result;
}
size_t getsize(void * p) {
size_t * in = p;
if (in) { --in; return *in; }
return -1;
}
#define malloc(_x) mymalloc((_x))
#define free(_x) myfree((_x))
void *reallocation(void *ptr,size_t size) {
void *newptr;
int msize;
msize = getsize(ptr);
printf("msize=%d\n", msize);
if (size <= msize)
return ptr;
newptr = malloc(size);
memcpy(newptr, ptr, msize);
free(ptr);
return newptr;
}
int main() {
char * aa = malloc(50);
char * bb ;
printf("aa size is %d\n",getsize(aa));
strcpy(aa,"my cookie");
bb = reallocation(aa,100);
printf("bb size is %d\n",getsize(bb));
printf("<%s>\n",bb);
free(bb);
}
Problem
``` int getmin(int a, int b) { return a<b?a:b; } void *reallocation(void *ptr, size_t size) //size_t in bytes { void *newptr; int msize; msize = getsize(ptr); msize = getmin(msize, size); printf("msize = %d", msize); newptr = malloc(size); newptr = memcpy(newptr, ptr, msize); free(ptr); return newptr; } ``` I have implemented my own realloc, and in order to get the size of the allocated memory using malloc(however i know there isn't any method for this in c). My reallocation function is working fine on my system How do we get the size of the memory allocated by malloc(). Also can we do inplace reallocation if the size of the previously allocated memory is greater than the new required?