zsh：总线错误。/array_stack 关于使用指针访问堆栈元素。 欢迎任何线索

Question

the code run fine when I used the dot operator for accessing the elements of the stack. But on using pointers to access the stack structure, I was getting this error. zsh: bus error./array_stack. Can anyone help me in resolving this.The code is as follows:

 #include<iostream>

 using namespace std;
//implementing the stack using an array

struct Stack{
int size;//size of the array
int top;//points to the last element of the array
int * arr;

};

int IsEmpty(struct Stack *ptr){
if(ptr->top == -1){
    return 1;
}
else{
    return 0;
}

 }

 int main(){
//one way of making the stack
// struct Stack S;
// S.size=43;
// S.top=-1;
// S.arr=(int *)malloc(S.size*sizeof(int));

//second way of making the stack
struct Stack *S;
S->size=54;
S->top=-1;
S->arr=(int *)malloc(S->size*sizeof(int));
if(IsEmpty(S)){
    cout<<"The array is empty.";
} 
return 0; 

}

Answer 1

EDIT: This question was originally tagged as C (not C++ ). I'm still not sure which way it will go. I will modify this answer to use C++ when it's clear.

The problem is you're defining S as a pointer to a Stack , but you never tell it to point to anything. So S is pointing to somewhere in memory (you probably don't own), and the S->size = 54 is trying to modify the content of that memory by writing 54 .

The fact that the code is generating a " Bus Error " indicates that S actually contains a memory address that is outside of valid memory range.

To fix it, S should be pointing at a stack:

struct Stack myStack;         // myStack is an actual stack
struct Stack *S = &myStack;   // a pointer to myStack

Obviously this method creates a Stack that is uninitialised. A nice way to do this sort of thing is to make a function that creates a new Stack , initialises it, then returns a pointer to it:

struct Stack *createStack( int capacity )
{
    assert( capacity > 0 );

    struct Stack *new_stack = malloc( sizeof( struct Stack ) );
    if ( new_stack != NULL )
    {
        new_stack->size = capacity;
        new_stack->top  = -1;
        new_stack->arr  = malloc( capacity * sizeof( int ) );  

        // If we failed to allocate array memory: clean-up & return NULL
        if ( new_stack->arr == NULL )
        {
            free( new_stack );
            new_stack = NULL;
        }
    }

    return new_stack;
}

Then in your code, it can be called:

struct Stack *s = createStack( 54 );