在 C 中何时使用按值传递与按右​​值引用传递？

按值传递和按右值引用传递的复杂性

简介：

在 C 中， pass 之间的选择按值或按右值引用传递可以显着影响函数的语义和效率。了解这两种参数传递机制之间的差异对于编写有效且高性能的代码至关重要。

按值传递与按右​​值引用传递

参数声明：

按值传递：

<code class="cpp">void foo(Widget w);
````

**Pass by Rvalue Reference:**</code>

void foo(Widget&& w);

#### Ownership Semantics:

* **Pass by Value:** Caller's object is copied into the function, and the copy is destroyed when the function exits. Ownership is transferred to the function.
* **Pass by Rvalue Reference:** Caller's object is moved into the function, and the caller relinquishes ownership. The moved object's resources are directly accessed within the function.

#### Implications for Interface:

* Pass by value implies that the caller expects the object to remain unchanged.
* Pass by rvalue reference suggests that the function may modify or destroy the object.

**Efficiency:**

* Pass by rvalue reference is potentially more efficient because it eliminates the need for an additional copy.
* Pass by value may result in a single move or copy constructor call, depending on the compiler's optimization level.

**Explicitness:**

* Pass by rvalue reference forces the caller to explicitly move the argument into the function, making the transfer of ownership clear.
* Pass by value implicitly copies the argument, which can lead to unexpected behavior if the intention is to move ownership.

### Conclusion:

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