What is the difference between using a struct with

问题:

What is the difference regarding memory allocation and efficiency between using a struct with two fields and a pair?

回答1:

std::pair provides pre-written constructors and comparison operators. This also allows them to be stored in containers like std::map without you needing to write, for example, the copy constructor or strict weak ordering via operator < (such as required by std::map). If you don't write them you can't make a mistake (remember how strict weak ordering works?) so it's more reliable just to use std::pair.

回答2:

std::pair comes with a number of constructors and operators.

A struct allow named fields (other than first and second) and is ready to be extended at any time.

Prefer a struct when you can. It may involve some overhead, but is definitely easier for maintenance.

回答3:

In terms of memory allocation and efficiency, there is no difference -- since that's exactly what a std::pair is.

回答4:

No difference in terms of memory allocation or efficiency. In fact, in the STL implementation I am using pair is defined as struct pair

回答5:

As stated in std::pair<int, int> vs struct with two int's a struct will probably be a little bit faster because no initialization is made.

回答6:

As this isn't mentioned above, if you want the benefits of your own name, but the advantages of std::pair (or any other objects), you can use ( from c++11 onwards). You can set this in your namespace or class declaration.

using myPair = pair<int,string>;

cf. C++ reference. for more documentation.