pushing structure variable in queue

Question

#include <iostream>
#include <queue>

using namespace std;

int main () {
    struct process {
        int burst;
        int ar;
    };
    int x=4;
    process a[x];
    queue <string> names; /* Declare a queue */
    names.push(a[1]);
    return 0;
}

I'm trying to pushing struct variable in queue but its not taking it and gives errors

no matching function for #include queue and invalid argument

how can I do that?

This is certainly a completely wrong approach: process a[x]; — πάντα ῥεῖ
– πάντα ῥεῖ, Commented May 9, 2015 at 18:09
@πάνταῥεῖ so u are saying i cant even create an array of structure? Because it does not give error {process a[x]} i have tested and also assigned burst and arrival to whole array and printed its working fine. — Rana Junaid Javed
– Rana Junaid Javed, Commented May 9, 2015 at 18:10
You can but that isn't how you create an array. What would the size even be? — Scott
– Scott, Commented May 9, 2015 at 18:13
You can do that, but your approach (to solve whatever) is pretty nonsensical and wrong (there's no, or just undefined memory allocated for a, snce x is uninitialized). — πάντα ῥεῖ
– πάντα ῥεῖ, Commented May 9, 2015 at 18:13
@Scott size is x which is i forget to initialize but in the other code where m working there is no error about process's array. — Rana Junaid Javed
– Rana Junaid Javed, Commented May 9, 2015 at 18:14

Community · Accepted Answer · 2017-05-23 12:06:33Z

0

C++ is a strongly typed language. In the line names.push(a[1]); you are trying to push a struct (from your process a[x]; array) into a queue<string>. Your struct is not a string, so the compiler will emit an error. You at least need a queue<process>.

Other issues: variable length arrays are not standard C++ (process a[x];). Use a std::vector<process> instead. Here is some simple example that works:

#include <iostream>
#include <queue>
#include <string>
#include <vector>

using namespace std;

int main () {
    struct process // move this outside of main() if you don't compile with C++11 support
    {
        int burst;
        int ar;
    };
    vector<process> a;
    // insert two processes
    a.push_back({21, 42});
    a.push_back({10, 20});

    queue <process> names; /* Declare a queue */
    names.push(a[1]); // now we can push the second element, same type
    return 0; // no need for this, really
}

EDIT

Locally defined classes/structs used to instantiate templates are valid only in C++11 and later, see e.g. Why can I define structures and classes within a function in C++? and the answers within. If you don't have access to a C++11 compliant compiler, then move your struct definition outside of main().

edited May 23, 2017 at 12:06

CommunityBot

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answered May 9, 2015 at 18:19

vsoftco

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4 Comments

Rana Junaid Javed Over a year ago

it is giving 4 errors at (vector<process> a;) 1.trying to instantiate 'template<class> class std::allocator 2. Invalid argument

vsoftco Over a year ago

Compile with -std=c++11

Rana Junaid Javed Over a year ago

thanks it really worked. I'm wondering if u tell me please why did u use a.push_back({21,42}) in the code. what is this ?

vsoftco Over a year ago

{21, 42} creates a temporary object of type struct process, which is then inserted in the vector via the push_back vector's member function. See e.g. this for a tutorial about std::vector.

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