Declaring queue in c++

Question

I'm trying to declare a queue in c++:

#include <queue>
......
......
queue<Process> *readyQueue = new queue<Process>;
.......

But i keep getting this error

'queue' was not declared in this scope

What am I missing? I, of course, created the Process struct, so the problem isn't there. What's the issue?

Do **not** use `new` unless you **know** you need to use `new`! I very much doubt you need to use `new`. C++ is not C# or Java. — Dietmar Kühl, Nov 03 '13 at 15:28
Your problem is that `std::queue` is declared in namespace `std`. — Dietmar Kühl, Nov 03 '13 at 15:28
@DietmarKühl when I add the std:: i get these errors, expected type-specifier before 'queue' cannot convert 'int*' to 'std::queue*' — zalyahya, Nov 03 '13 at 15:35
@user1929226 maybe you're tryin to do something like `readyQueue.push(/* int* type */);` — Netherwire, Nov 03 '13 at 15:40
@user1929226: Given the mutilated example, I can't tell what your code would look like, but I do know that `std::queue` should work better than `queue`. — Dietmar Kühl, Nov 03 '13 at 15:43

score 19 · Answer 1 · answered Nov 03 '13 at 15:37

19

You are missing namespace specification. I suppose you want std functions. Use either:

 #include <queue>
 ......
 std::queue<Process> *readyQueue = new std::queue<Process>;

or

 #include <queue>
 using std::queue;
 ......
 queue<Process> *readyQueue = new queue<Process>;

answered Nov 03 '13 at 15:37

klm123

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Can whoever downvoted this answer comment on the reason for the downvote? Given that the fix is the correct fix, it is entirely unwarranted. – Dietmar Kühl Nov 03 '13 at 15:44

score 8 · Answer 2 · answered Nov 03 '13 at 15:35

8

You need to specify the correct namespace

std::queue

answered Nov 03 '13 at 15:35

John Dibling

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when i do so, i get these errors: expected type-specifier before 'queue' cannot convert 'int*' to 'std::queue*' – zalyahya Nov 03 '13 at 15:37
1

A whole othef problem. – John Dibling Nov 03 '13 at 15:37

score 7 · Answer 3 · answered Nov 03 '13 at 15:35

7

You should use using namespace std; or the std:: prefix. This might help you:

#include <queue>

int main()
{
    Process p1;
    Process p2;

    std::queue<Process> readyQueue;
    readyQueue.push(p1);
    readyQueue.push(p2);
}

See reference for more details.

answered Nov 03 '13 at 15:35

Netherwire

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[`using namespace std`](http://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) is not so cool. Other than that the answer is completely correct. – juanchopanza Nov 03 '13 at 15:46
@juanchopanza, you're right. Just an another option. In ordinary, i'm trying to avoid this at all and use std:: prefix. – Netherwire Nov 03 '13 at 17:23

Declaring queue in c++

3 Answers3