> 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/functions/parameter-passing.md).

# 函数参数传递

C++ 的函数参数有三种传递方式：**值传递**、**引用传递**、**指针传递**。

### 值传递

传递的是实参的**副本**，函数内修改不影响原变量。

```cpp
void addOne(int x) { x++; }

int a = 5;
addOne(a);
cout << a;  // 仍是 5
```

### 引用传递

形参加 `&`，是实参的**别名**，函数内修改会影响原变量。

```cpp
void addOne(int &x) { x++; }

int a = 5;
addOne(a);
cout << a;  // 6
```

### 指针传递

传递变量地址，通过解引用修改原变量。

```cpp
void addOne(int *p) { (*p)++; }

int a = 5;
addOne(&a);
cout << a;  // 6
```

### 三者对比

| 方式   | 形参写法     | 能否改变实参 | 传大对象效率 |
| ---- | -------- | ------ | ------ |
| 值传递  | `int x`  | 否      | 低（要复制） |
| 引用传递 | `int &x` | 是      | 高      |
| 指针传递 | `int *x` | 是      | 高      |

常用技巧：传大数组 / 字符串时用 `const 引用`，如 `const string &s`，既高效又不会被修改。


---

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