详解C语言指针（上）：(含大厂面试实战哦！）指针运算、指针和数组、多级函数

变量地址 = &变量
变量值 = *地址

int arr[5] = {0};
int *p = arr;
p++; // 实际移动sizeof(int)字节

int a[5] = {1,2,3,4,5};
int *ptr = (int *)(&a + 1);
printf("%d %d", *(a+1), *(ptr-1)); 

void (*signal(int sig, void (*func)(int)))(int);
// 请解析这个函数声明

// 排序回调示例
void qsort(void *base, size_t nmemb, size_t size,
           int (*compar)(const void *, const void *));

int a = 10;
int *p = &a;
int **pp = &p;
int ***ppp = &pp;

printf("%d", ***ppp++); 

char arr[] = "hello";
char *p = "hello";

printf("%zu %zu", sizeof(arr), sizeof(p)); 

char *get_str() {
    char str[] = "hello";
    return str; // 为什么不能这样返回？
}

#define malloc(size) debug_malloc(size, __FILE__, __LINE__)
#define free(ptr) debug_free(ptr, __FILE__, __LINE__)

// 反转单链表
struct Node 
{
    int data;
    struct Node* next;
};

struct Node* reverse(struct Node* head) 
{
    struct Node *prev = NULL, *current = head, *next = NULL;
    while (current) 
    {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    return prev;
}

const int *p;       // 指向常量的指针
int const *p;       // 同上
int * const p;      // 常量指针
const int * const p;// 指向常量的常量指针

// 不用临时变量交换两个数
void swap(int *a, int *b) 
{
    *a ^= *b;
    *b ^= *a;
    *a ^= *b;
}

int main() 
{
    int a[5] = {1,2,3,4,5};
    int *p1 = (int*)(&a + 1);
    int *p2 = (int*)((int)a + 1);
    printf("%x %x", p1[-1], *p2); 
}