Index
Description
The C library function void realloc(void \*ptr, size) attempts to resize the memory block pointed to by ptr that was previously allocated with a call to malloc or calloc.
If there isn’t enough memory space in the previous position, the function may move the memory block to a new location (whose address is returned by the function).
Syntax
void *realloc(void *ptr, size)-
ptr − This is the pointer to a memory block previously allocated with malloc, calloc or realloc to be reallocated. If this is NULL, a new block is allocated and a pointer to it is returned by the function.
-
size − This is the new size for the memory block, in bytes. If it is 0 and ptr points to an existing block of memory, the memory block pointed by ptr is deallocated and a NULL pointer is returned.
Return Value
- This function returns a pointer to the newly allocated memory oss: non c’è bisogno di fare il controllo per vedere s l’operazione è andata a buon fine (la C malloc Function ne ha bisogno)
Computational Cost
- Constant O(1)
- Linear O(n), if needs to reallocate the memory (worsts case)
Example
realloc:
array_int array_int_append( array_int v, int e ){
// aggiunge un elemento in coda all'array di interi
if (v.n == v.c){ // Controllo se l'array è pieno
v.a = realloc(v.a, (2*v.c+1)*sizeof(int));
v.c = 2*v.c+1;
}
v.a[v.n] = e; // inserimento dell'elemento
v.n++; // incremento il numero di elementi
return v;
}Same example but using malloc:
array_int array_int_append( array_int v, int e ){
int i;
int *a;
if ( v.n == v.c ){
a = malloc((2*v.c+1)*sizeof(int));
if (a == NULL)
return v;
for(i = 0; i < v.n; i++){
a[i] = v.a[i];
}
v.c = 2*v.c+1;
free(v.a);
v.a = a;
}
v.a[v.n] = e;
v.n++;
return v;