sizeof(structname) is this wrong? - c

Question

Windows has triggered a breakpoint in Graph.exe.
This may be due to a corruption of the heap, which indicates a bug in Graph.exe or any of the DLLs it has loaded.
This may also be due to the user pressing F12 while Graph.exe has focus.
The output window may have more diagnostic information
I don't have any breakpoint in my code and I don't pressed F12.
this is my code.
what's wrong?
printf("sizeof edge : %d\n",sizeof(edge));this line make that error.
I can't understand why
what's wrong?
#include <stdio.h>
#include <stdlib.h>
typedef struct HeapStruct heap;
typedef struct edge edge;
struct edge
{
int start,end,weight;
};
struct HeapStruct {
int Capacity;
int Size;
edge *head;
};
void init(int * sets,int size);
int unionsets(int * sets, int i, int j);
int find(int * sets, int i);
void buildHeap(heap h);
edge deleteMin(heap * h);
int ends(int * sets,int size);
int main()
{
int V,E,*sets,a,startv,endv,weight;
char c,h;
edge ed;
edge * ee;
heap * Heap;
Heap = (heap*)malloc(sizeof(heap));
printf("sizeof edge : %d\n",sizeof(edge));//this line
scanf("%d",&V);
sets = (int*)malloc(sizeof(int)*V);
init(sets,V);
scanf("%d",&E);
Heap->head = (edge*)malloc(sizeof(edge)*E);//and this line
Heap->Capacity = E;
Heap->Size=0;
for(a=0; a<E; a++)
{
scanf("%d%c%d%c%d",&startv,&c,&endv,&h,&weight);
Heap->head[Heap->Size].end = endv;
Heap->head[Heap->Size++].start = startv;
Heap->head[Heap->Size++].weight = weight;
}
buildHeap(*Heap);
do
{
ed = deleteMin(Heap);
if(find(sets,ed.start)<0 || find(sets,ed.end)<0 || find(sets,ed.start) != find(sets,ed.end))
{
unionsets(sets,ed.start,ed.end);
printf("%d,%d,%d\n",ed.start,ed.end,ed.weight);
}
}
while(ends(sets,V));
scanf("%d%c%d%c%d",&startv,&c,&endv,&h,&weight);
return 0;
}

Answer 1

Windows has triggered a breakpoint in Graph.exe.
It is literally what it says, the operating system itself made the debugger stop. When you debug your program on any recent Windows version then you get the debug version of the Windows memory manager. Which adds extra checks that ensure that your program isn't corrupting the heap. When it detects heap damage then it breaks the program to tell you about it.
Very useful. What you need to do next is to carefully review your code to make sure it isn't writing to memory that wasn't allocated. You'll then land on this statement:
Heap->head[Heap->Size++].start = startv;
Which along with the other statements in that code assumes that this array contains 3 * E elements but you allocated only E elements.
Kaboom!

Answer 2

printf("sizeof edge : %d\n",sizeof(edge));
This can crash a 64-bit system, because sizeof returns a 64-bit number but %d expects only 32 bits. Try %zd instead.
Yep, C is finicky. Your compiler should have given a warning about this, though.