在给函数使用原始变量时，更好的做法是什么:
unsigned long x = 4;
void func1(unsigned long& val) {
val = 5;
}
func1(x);
or:
void func2(unsigned long* val) {
*val = 5;
}
func2(&x);
勒夫:有什么理由选择一个而不是另一个吗?
当前回答
考虑一下c#的out关键字。编译器要求方法的调用者将out关键字应用于任何out参数，即使它已经知道它们是否存在。这是为了提高可读性。尽管在现代ide中，我倾向于认为这是语法(或语义)突出显示的工作。
其他回答
如果你要修改变量的值，你应该传递一个指针。 尽管在技术上传递引用或指针是相同的，但在用例中传递指针更具有可读性，因为它“通告”了函数将更改值的事实。
引用是隐式指针。基本上，你可以改变引用指向的值，但你不能改变引用指向其他东西。因此，我的观点是，如果你只想改变一个参数的值，将其作为引用传递，但如果你需要改变参数以指向一个不同的对象，则使用指针传递它。
这最终是主观的。到目前为止的讨论是有用的，但我不认为有一个正确或决定性的答案。这在很大程度上取决于风格指南和您当时的需求。
While there are some different capabilities (whether or not something can be NULL) with a pointer, the largest practical difference for an output parameter is purely syntax. Google's C++ Style Guide (https://google.github.io/styleguide/cppguide.html#Reference_Arguments), for example, mandates only pointers for output parameters, and allows only references that are const. The reasoning is one of readability: something with value syntax should not have pointer semantic meaning. I'm not suggesting that this is necessarily right or wrong, but I think the point here is that it's a matter of style, not of correctness.
通过const引用传递，除非有原因你希望改变/保留你传递的内容。
在大多数情况下，这将是最有效的方法。
确保对不想更改的每个形参都使用const，因为这不仅可以防止您在函数中做一些愚蠢的事情，还可以很好地向其他用户指示函数对传入的值做了什么。这包括当你只想改变所指向的对象时，创建一个const指针…
我真的认为你将受益于建立以下函数调用编码指南:
As in all other places, always be const-correct. Note: This means, among other things, that only out-values (see item 3) and values passed by value (see item 4) can lack the const specifier. Only pass a value by pointer if the value 0/NULL is a valid input in the current context. Rationale 1: As a caller, you see that whatever you pass in must be in a usable state. Rationale 2: As called, you know that whatever comes in is in a usable state. Hence, no NULL-check or error handling needs to be done for that value. Rationale 3: Rationales 1 and 2 will be compiler enforced. Always catch errors at compile time if you can. If a function argument is an out-value, then pass it by reference. Rationale: We don't want to break item 2... Choose "pass by value" over "pass by const reference" only if the value is a POD (Plain old Datastructure) or small enough (memory-wise) or in other ways cheap enough (time-wise) to copy. Rationale: Avoid unnecessary copies. Note: small enough and cheap enough are not absolute measurables.
