为什么我这个地址在主 function 初始化后被更改？ （C）

Question

I'm new to C and I'm facing some problems with a project I am working on.

In vm.h

#define STACK_MAX 256
typedef double Value;

typedef struct {
   Value values[STACK_MAX];
   Value* top;
}

typedef struct {
   Chunk* chunk;
   uint8_t* ip; // Instruction pointer
   Stack stack;
} VM;

VM initVm();
void resetStack(Stack* stack);

In vm.c

void resetStack(Stack* stack) {
    stack->top = stack->values
}

VM initVM() {
    VM vm;
    resetStack(&vm.stack);
    return VM;
}

In main.c

int main() {
    VM vm = initVM();

    ... 
}

Ok, here's the problem. After I initialize vm, vm.stack.top is pointing to vm.stack.values[0] (which I don't know why is filled with garbage values instead of zeroes), but one instruction later, no matter what, vm.stack.top is changed and starts pointing something else or sometimes the address of the vm.stack.values[0] is changed to another.

Answer 1

The problem was VM was declared in the local scope. Allocating VM in the heap solved it.