通過設置指針初始化在C語言的堆疊爲NULL

Question

我試圖根據下面的頭（stack.h）用C來實現堆棧：

#ifndef STACK_H 
#define STACK_H 

/* An element from which stack is consisting */ 
typedef struct stack_node_ss { 
    struct stack_node_ss *next; /* pointer to next element in stack */ 
    void *value;     /* value of this element */ 
} stack_node_s; 

/* typedef so that stack user doesn't have to worry about the actual type of 
* parameter stack when using this stack implementation. 
*/ 
typedef stack_node_s* stack_s; 

/* Initializes a stack pointed by parameter stack. User calls this after he 
* has created a stack_t variable but before he uses the stack. 
*/ 
void stack_init(stack_s *stack); 

/* Pushes item to a stack pointed by parameter stack. Returns 0 if succesful, 
* -1 otherwise. 
*/ 
int stack_push(void *p, stack_s *stack); 

/* Pops item from a stack pointed by parameter stack. Returns pointer to 
* element removed from stack if succesful, null if there is an error or 
* the stack is empty. 
*/ 
void *stack_pop(stack_s *stack); 

#endif 

然而，作爲新帶C，我停留在stack_init功能，我已經寫在stack.c：

#include <stdlib.h> 
#include <stdio.h> 
#include "stack.h" 

void stack_init(stack_s *stack) { 
    (*stack)->value = NULL; 
    (*stack)->next = NULL; 
} 

主程序開頭：

int *tmp; 
    stack_s stack; 
    stack_init(&stack); 

而這種崩潰我的程序與：

Program received signal EXC_BAD_ACCESS, Could not access memory. 
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000008 
0x0000000100000abf in stack_init (stack=0x7fff5fbffb30) at stack.c:6 
6  (*stack)->value = NULL; 

你可以暗示我到正確的軌道嗎？非常感謝。

Answer 1

你必須爲自己**stack分配內存：

*stack = malloc(sizeof(**stack)); 

但請不要typedef定義指針類型。這真是令人困惑，難以閱讀。更好地按值傳遞指針，它留給調用者來存儲指針，就像這樣：

typedef struct stack_node_t 
{ 
    struct stack_node_t * next; 
    /* ... */ 
} stack_node; 

stack_node * create_stack() 
{ 
    stack_node * res = calloc(1, sizeof(stack_node)); 
    return res; 
} 

void destroy_stack(stack_node * s) 
{ 
    if (!next) return; 

    stack_node * next = s->next; 
    free(s); 
    destroy_stack(next); 
} 

// etc. 

然後，你可以說：

stack_node * s = create_stack(); 

// use s 

destroy_stack(s); 
s = NULL; // some people like this 

Answer 2

您正在訪問一個未初始化的指針，造成不確定行爲。

因爲這個功能是創建一個新的堆棧，您需要分配一些動態內存堆棧，然後將指針指向新分配的內存：

void stack_init(stack_s *stack) { 
    *stack = malloc(sizeof(**stack)); // create memory for the stack 

    (*stack)->value = NULL; 
    (*stack)->next = NULL; 
} 

stack_s stack; 
stack_init(&stack); 

那麼你應該有一個調用的函數stack_destroy將free的動態內存，並設置指針NULL：

​​

Answer 3

你應該堆棧初始化爲NULL - 不爲NULL值推到它：

void stack_init(stack_s *stack) { 
    *stack=NULL; 
}