我了解指针和引用的语法和一般语义,但是我应该如何决定什么时候在API中使用引用或指针比较合适?

当然,有些情况需要其中一个(操作符++需要引用参数),但一般来说,我发现我更喜欢使用指针(和const指针),因为语法很清楚,变量是破坏性传递的。

例如,在以下代码中:

void add_one(int& n) { n += 1; }
void add_one(int* const n) { *n += 1; }
int main() {
  int a = 0;
  add_one(a); // Not clear that a may be modified
  add_one(&a); // 'a' is clearly being passed destructively
}

使用指针,它总是(更)明显的发生了什么,所以对于api和类似的地方,清晰度是一个大问题,指针不是比引用更合适吗?这是否意味着引用应该只在必要时使用(例如操作符++)?其中一种是否存在性能问题?

编辑(过时的):

除了允许NULL值和处理原始数组之外,选择似乎还取决于个人喜好。我接受下面的答案,引用谷歌的c++风格指南,因为他们提出的观点是“引用可能会令人困惑,因为它们有值语法,但有指针语义。”

由于需要额外的工作来清除不应该为NULL的指针参数(例如,add_one(0)将调用指针版本并在运行时中断),从可维护性的角度来看,在必须存在对象的地方使用引用是有意义的,尽管失去语法的清晰性是一种遗憾。


当前回答

从 C++ 常见问题精简版 -

Use references when you can, and pointers when you have to. References are usually preferred over pointers whenever you don't need "reseating". This usually means that references are most useful in a class's public interface. References typically appear on the skin of an object, and pointers on the inside. The exception to the above is where a function's parameter or return value needs a "sentinel" reference — a reference that does not refer to an object. This is usually best done by returning/taking a pointer, and giving the NULL pointer this special significance (references must always alias objects, not a dereferenced NULL pointer). Note: Old line C programmers sometimes don't like references since they provide reference semantics that isn't explicit in the caller's code. After some C++ experience, however, one quickly realizes this is a form of information hiding, which is an asset rather than a liability. E.g., programmers should write code in the language of the problem rather than the language of the machine.

其他回答

这不是品味的问题。以下是一些明确的规则。

如果你想在声明变量的范围内引用静态声明的变量,那么使用c++引用,这将是完全安全的。这同样适用于静态声明的智能指针。通过引用传递参数就是一个例子。

如果你想从一个比它声明的范围更宽的范围中引用任何东西,那么你应该使用一个引用计数智能指针,以确保它的完全安全。

为了语法方便,您可以使用引用引用集合的元素,但这并不安全;元素可以在任何时候被删除。

为了安全地保存对集合元素的引用,必须使用引用计数智能指针。

对于指针,您需要它们指向某个对象,因此指针需要占用内存空间。

例如,接受整数指针的函数将不接受整数变量。因此,您需要首先为它创建一个指针,以便传递给函数。

作为参考,它不会占用内存。你有一个整数变量,你可以把它作为引用变量传递。就是这样。您不需要专门为它创建引用变量。

在我的实践中,我个人确定了一个简单的规则——对可复制/可移动的原语和值使用引用,对具有长生命周期的对象使用指针。

对于Node的例子,我肯定会使用

AddChild(Node* pNode);

从 C++ 常见问题精简版 -

Use references when you can, and pointers when you have to. References are usually preferred over pointers whenever you don't need "reseating". This usually means that references are most useful in a class's public interface. References typically appear on the skin of an object, and pointers on the inside. The exception to the above is where a function's parameter or return value needs a "sentinel" reference — a reference that does not refer to an object. This is usually best done by returning/taking a pointer, and giving the NULL pointer this special significance (references must always alias objects, not a dereferenced NULL pointer). Note: Old line C programmers sometimes don't like references since they provide reference semantics that isn't explicit in the caller's code. After some C++ experience, however, one quickly realizes this is a form of information hiding, which is an asset rather than a liability. E.g., programmers should write code in the language of the problem rather than the language of the machine.

正确编写的示例应该如下所示

void add_one(int& n) { n += 1; }
void add_one(int* const n)
{
  if (n)
    *n += 1;
}

这就是为什么推荐信在可能的情况下更可取 ...