realloc is overwriting half of chunk of memory with 0xFEEEFEEE-CodePudding

I'm currently implementing a stack data structure in C. I was testing the portion of code responsible for realloc'ing the stack's memory when it runs out of space to push more data on. Here is the code I am using to test it:

#include <stdlib.h>
#include <stdbool.h>

typedef struct
{
    int* mem;
    int size;
    int top;
} Stack;

bool Stack_Init(Stack* stack, int size)
{
    stack->mem = malloc(size * sizeof(int));
    if (!stack->mem)
    {
        return false;
    }

    stack->size = size;
    stack->top = -1;
    return true;
}

void Stack_Push(Stack* stack, int data)
{
    stack->top  ;
    if (stack->top >= stack->size)
    {
        stack->mem = realloc(stack->mem, stack->size * 2);
        stack->size *= 2;
    }

    stack->mem[stack->top] = data;
}

int main(void)
{
    Stack stack;
    Stack_Init(&stack, 256);

    // I set the condition to i < 257 so that the final loop triggers a realloc
    for (int i = 0; i < 257; i  )
    {
        Stack_Push(&stack, i);
    }
}

When running my code through GDB, near the end I recieved a warning:

warning: HEAP[Test.exe]:
warning: HEAP: Free Heap block 0000028B44EE17B0 modified at 0000028B44EE1990 after it was freed

I know I should be checking realloc return value, but that doesn't appear to be the problem. The thing that I can't figure out is that before the realloc in Stack_Push, examining stack->mem shows nothing out of order, but after the realloc, the second half of stack->mem (after 128 bytes) is overwritten with some random garbage and a lot of 0xFEEEFEEE. You can see what I'm talking about here:

0x20eb8571590:  0x00000000      0x00000001      0x00000002      0x00000003
0x20eb85715a0:  0x00000004      0x00000005      0x00000006      0x00000007
0x20eb85715b0:  0x00000008      0x00000009      0x0000000a      0x0000000b
0x20eb85715c0:  0x0000000c      0x0000000d      0x0000000e      0x0000000f
0x20eb85715d0:  0x00000010      0x00000011      0x00000012      0x00000013
0x20eb85715e0:  0x00000014      0x00000015      0x00000016      0x00000017
0x20eb85715f0:  0x00000018      0x00000019      0x0000001a      0x0000001b
0x20eb8571600:  0x0000001c      0x0000001d      0x0000001e      0x0000001f
0x20eb8571610:  0x00000020      0x00000021      0x00000022      0x00000023
0x20eb8571620:  0x00000024      0x00000025      0x00000026      0x00000027
0x20eb8571630:  0x00000028      0x00000029      0x0000002a      0x0000002b
0x20eb8571640:  0x0000002c      0x0000002d      0x0000002e      0x0000002f
0x20eb8571650:  0x00000030      0x00000031      0x00000032      0x00000033
0x20eb8571660:  0x00000034      0x00000035      0x00000036      0x00000037
0x20eb8571670:  0x00000038      0x00000039      0x0000003a      0x0000003b
0x20eb8571680:  0x0000003c      0x0000003d      0x0000003e      0x0000003f
0x20eb8571690:  0x00000040      0x00000041      0x00000042      0x00000043
0x20eb85716a0:  0x00000044      0x00000045      0x00000046      0x00000047
0x20eb85716b0:  0x00000048      0x00000049      0x0000004a      0x0000004b
0x20eb85716c0:  0x0000004c      0x0000004d      0x0000004e      0x0000004f
0x20eb85716d0:  0x00000050      0x00000051      0x00000052      0x00000053
0x20eb85716e0:  0x00000054      0x00000055      0x00000056      0x00000057
0x20eb85716f0:  0x00000058      0x00000059      0x0000005a      0x0000005b
0x20eb8571700:  0x0000005c      0x0000005d      0x0000005e      0x0000005f
0x20eb8571710:  0x00000060      0x00000061      0x00000062      0x00000063
0x20eb8571720:  0x00000064      0x00000065      0x00000066      0x00000067
0x20eb8571730:  0x00000068      0x00000069      0x0000006a      0x0000006b
--Type <RET> for more, q to quit, c to continue without paging--c
0x20eb8571740:  0x0000006c      0x0000006d      0x0000006e      0x0000006f
0x20eb8571750:  0x00000070      0x00000071      0x00000072      0x00000073
0x20eb8571760:  0x00000074      0x00000075      0x00000076      0x00000077
0x20eb8571770:  0x00000078      0x00000079      0x0000007a      0x0000007b
0x20eb8571780:  0x0000007c      0x0000007d      0x0000007e      0x0000007f
0x20eb8571790:  0xabababab      0xabababab      0xabababab      0xabababab
0x20eb85717a0:  0x00000000      0x00000000      0x00000000      0x00000000
0x20eb85717b0:  0x00000088      0x00000089      0x741cb74f      0x0000c15d
0x20eb85717c0:  0xb8574450      0x0000020e      0xb8570150      0x0000020e
0x20eb85717d0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85717e0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85717f0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571800:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571810:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571820:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571830:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571840:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571860:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571870:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571880:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571890:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85718a0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85718b0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85718c0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85718d0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85718e0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb85718f0:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571900:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571910:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571920:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571930:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571940:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571950:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571960:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571970:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571980:  0xfeeefeee      0xfeeefeee      0xfeeefeee      0xfeeefeee
0x20eb8571990:  0xfeeefeee

I'm unsure what could be causing this, as I can't seem to see anything wrong with the code and after running it with a debugger multiple times I still don't see what is causing it.

CodePudding user response：

stack->mem = realloc(stack->mem, stack->size * 2);

Here you should multiply with sizeof(int)

stack->mem = realloc(stack->mem, sizeof(int)*stack->size * 2);