I am trying to implement a dinamically increasing array with realloc. I create the array with malloc, and then call my add function, which increases the array size by 1. Here's the code:
#include <stdio.h>
#include <stdlib.h>
int *foo;
int quantity;
void add(int number) {
foo = (int*) realloc(foo, sizeof(foo) + sizeof(int));
foo[quantity] = number;
quantity++;
}
void debugFoo() {
for (int i = 0; i < quantity; i++) {
printf("foo[%i] = %i\n", i, foo[i]);
}
printf("\n");
}
int main() {
quantity = 3;
foo = (int*) malloc(quantity * sizeof(int));
foo[0] = 1;
foo[1] = 2;
foo[2] = 3;
debugFoo();
add(20);
debugFoo();
add(2);
debugFoo();
return 0;
}
However when I run it, I get the following output:
foo[0] = 1
foo[1] = 2
foo[2] = 3
foo[0] = 1
foo[1] = 2
foo[2] = 3
foo[3] = 20
foo[0] = 1
foo[1] = 2
foo[2] = 3
foo[3] = 21
foo[4] = 2
As you can see, the value of foo[3] is incremented by 1 the second time I call add. And the odd thing is that it is only incremented if the first value passed to add is even. Changing line 30 to add(21), I get the following output:
[...]
foo[2] = 3
foo[3] = 21
foo[0] = 1
foo[1] = 2
foo[2] = 3
foo[3] = 21
foo[4] = 2
Is this a bug or am I using realloc wrong?
sizeof(foo) is not the size of allocated buffer but the size of foo, which is int*. Use saved number of elements to calculate new buffer size.
foo = (int*) realloc(foo, sizeof(int) * (quantity + 1));