How to access member elements of a std::queue data structure? [duplicate] - c++

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Compilation Error: void value not ignored as it ought to be in std::queue::pop() [duplicate]
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Invalid use of void expression with a Queue and .pop()
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Why doesn't std::queue::pop return value.?
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Closed 2 years ago.
Coding in C+, using Visual Studio 2019, I have a structure defined. I am creating a queue of that data structure and have pushed 2 elements into the queue. Now the question is how to access the members of the structure elements inside the queue?? Any guidance is appreciated!
#include <iostream>
#include <sstream>
#include <cstdlib>
#include <queue>
typedef struct _myqueuestruct
{
string name;
int citypin;
int employeeId;
}myqueuestruct;
int main()
{
queue<myqueuestruct> myQ;
myqueuestruct myQelement;
myQelement.name = "Harry";
myQelement.citypin = "Ohio";
myQelement.employeeId = "345";
// Insert some elements into the queue
myQ.push(myQelement);
myQelement.name = "John";
myQelement.citypin = "Jaipur";
myQelement.employeeId = "223";
// Insert some elements into the queue
myQ.push(evtSvcElement);
//myQ.size();
//queue<myqueuestruct>::iterator it = myQ.begin();
for (int i = 0; i < myQ.size(); i++)
{
cout << myQ.front();
myQ.pop(); //???? How do I access the member values of the elements of the queue?
}
while (1);
return 0;
}

Answer 1

Well, front returns a reference to the first element, so like this:
std::cout << myQ.front().name; // and similarly for other elements
Or, for example, make a referenence yourself:
auto& ref = myQ.front();
ref.name = "foo";
ref.citypin = 42;
// etc.

Answer 2

I have modified your code to get it compiling and working: (Note: I have used C++17 standard using g++ to compile this code but it should work for visual studio 2019
#include <iostream>
#include <queue>
typedef struct _myqueuestruct
{
std::string name;
std::string citypin;
int employeeId;
}myqueuestruct;
int main()
{
std::queue<myqueuestruct> myQ;
myqueuestruct myQelement;
myQelement.name = "Harry";
myQelement.citypin = "Ohio";
myQelement.employeeId = 345;
// Insert some elements into the queue
myQ.push(myQelement);
myQelement.name = "John";
myQelement.citypin = "Jaipur";
myQelement.employeeId = 223;
// Insert some elements into the queue
myQ.push(myQelement);
while (myQ.size() > 0)
{
auto & e = myQ.front();
std::cout << "Name: " << e.name
<< " CityPin: " << e.citypin
<< " EmployeeId: " << e.employeeId << std::endl;
myQ.pop();
}
return 0;
}
I would like to point out a few changes I have to make in your above code:
in your struct definition you used int datatype but you assigned char string to the same. I have modified the datatype to be std::string.
using while loop for iterating through all the elements and using myQ.size() every time instead of using for loop.
std::cout - holding the element reference in a local variable inside the loop and printing all member variables.
Improvements you can make to above code:
There are multiple transient copies of the object being created when you push the object into the queue. I would suggest refer std::queue documentation here: http://www.cplusplus.com/reference/queue/queue/ and try to enhance above code with
emplace_back
overload operator<< for your class for printing class members, this would help you learn about operator overloading.