将Windows代码移植到Mac

Question

I'm migrating C++ code from Windows to Mac. I choose OS X Command line Tool with language C++.

Here is the code snippet:

    #ifndef __PRIORITYQUEUE_H__
    #define __PRIORITYQUEUE_H__
    #include <queue>

    template <typename T, class Container = std::vector<T>, class Compare = std::less<typename Container::value_type>>
    class PriorityQueue : public std::priority_queue<T, Container, Compare>
    {
    public:
        PriorityQueue() {}
        PriorityQueue(const PriorityQueue& pq) {priority_queue(pq);}   // line:13
        explicit PriorityQueue(const Compare& compare) {priority_queue(compare);}
        PriorityQueue(const Compare& compare, const Container& container) {priority_queue(compare, container);}
        template<class Iter> PriorityQueue(Iter first, Iter last) {priority_queue(first, last);}
        template<class Iter> PriorityQueue(Iter first, Iter last, const Compare& compare) {priority_queue(first, last, compare);}
        template<class Iter> PriorityQueue(Iter first, Iter last, const Compare& compare, const Container& container) {priority_queue(first, last, compare, container);}
    ......
    #endif

And there are other files will include this header file. When I compile it, the following error happens:

1. /Users/yingyhe/Projects/SASCode/SASPRLib/PriorityQueue.h:13:53: Unknown type name 'priority_queue'; did you mean 'PriorityQueue'?
2. /Users/yingyhe/Projects/SASCode/SASPRLib/PriorityQueue.h:13:68: Redefinition of 'pq'

It seems this header file isincluded multiple times, but I've used #ifndef - #define - #endif to avoid that.

Then I take this header file to a new project, and no other file include it, and it can compile successfully. It's wired, anyone can tell me why? Many Thanks!!!

Answer 1

You forgot the std:: prefix.

I suspect that you usually include this file where you're also using namespace std; prior to its inclusion.

But there are more problems.

First of all, the standard library containers are not made for use as base classes.
Don't do it.

Base classes are initialised in the initialiser list , not in the constructor body like in eg Java:

PriorityQueue(const PriorityQueue& pq) : std::priority_queue(pq) {} 

You get the redefinition error because you're declaring a local variable with the same name as the parameter.

In the body of a function,

std::priority_queue(pq);

is equivalent to

std::priority_queue pq;

This follows the "if it could be a declaration, it is a declaration" rule.

If no other file includes the header, it won't be compiled at all, which it why it works in that case.
It will be compiled once for each source file it is included in, which is as expected - "include guards" guard against multiple inclusions in a translation unit , and each translation unit is compiled separately.

Answer 2

I changed line 13 to this:

`PriorityQueue(const PriorityQueue& pq) : priority_queue<T, Container, Compare>(pq) {}`

and it's pass the compile