> For the complete documentation index, see [llms.txt](https://docs.1l.lol/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.1l.lol/basics/pointers.md).

# 指针

### 指针是什么

指针是一个**存放地址**的变量。普通变量存数据，指针变量存“某数据在哪”。

```cpp
int a = 10;
int *p = &a;   // p 存放 a 的地址
cout << *p;    // 10，* 解引用，访问 p 指向的变量
*p = 20;       // 通过指针修改 a
```

### 两个核心运算符

* `&` 取地址：`&a` 得到变量 a 的地址
* `*` 解引用：`*p` 访问 p 指向的值

### 指针与数组

数组名本质上是首元素地址，`a[i]` 等价于 `*(a + i)`。

```cpp
int a[3] = {10, 20, 30};
int *p = a;
cout << *p << endl;       // 10
cout << *(p + 2) << endl; // 30
cout << p[1] << endl;     // 20
```

### 指针的算术

`p + 1` 不是加 1 字节，而是跳到**下一个同类型元素**，移动 `sizeof(类型)` 字节。

### 空指针

```cpp
int *p = nullptr;   // 不指向任何地址
if (p == nullptr) cout << "空指针";
```

### 指针与结构体

用 `->` 通过结构体指针访问成员：

```cpp
struct Node { int a; string s; };
Node n{5, "hi"};
Node *p = &n;
cout << p->a << " " << p->s;   // 5 hi
```

### 常见用途

* 函数参数传递（指针传递，可修改实参）
* 动态内存分配（`new` / `delete`）
* 构建链表、树等动态数据结构

> 陷阱：野指针（未初始化的指针）解引用会崩溃；指针指向的数组越界是未定义行为。


---

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