CODEWITHSUNDEEP
c++templatesvector
Hummingbird
Hummingbird

Reputation: 645

size of a static vector

I am using a static vector inside a member function and pushing back values into that vector; but the size of vector is only 1 for three function calls.

I am not sure how to make MVCE for this as in MVCE it is working fine for me too, so the problem is obviously some other part of code. I just want to know or have an idea under which circumstances would my static vector give me such results.

class X
{
    //...
};

template <typename T>
void test(T a)
{
    std::cout<<"Function called \n";
    static std::vector<X> vec;
    std::lock_guard<std::mutex> lock(mx);
    //Doing something else with T
    X obj;
    vec.push_back(obj);
    std::cout<<"no of elements in vec is "<<vec.size()<<"\n";

}

The output coming is 

Function called 
no of elements in vec is 1
Function called 
no of elements in vec is 1
Function called 
no of elements in vec is 1

The member function is called from the CPPREST http_client request call.

Upvotes: 4

Views: 1205

Answers (2)

Stan Holodnak
Stan Holodnak

Reputation: 105

Your request call probably looks similar to this int i = 1; float f = 2.5; char c = 'A'; test(i); test(f); test(c);

If you add test(i);

Then vec.size() for test(int) will be 2 While vec.size() for test(float) and test(char) will stay 1.

You can read more about the behavior of static variables in templates here http://www.geeksforgeeks.org/templates-and-static-variables-in-c/

Upvotes: 2

songyuanyao
songyuanyao

Reputation: 172924

Note that the template instantiations with different type are irrelevant. It means if you called test() three time with different type T, then three irrelevant test() will be instantiated, with 3 diffrent instances of vec. That's why you're getting the result that their size are all 1.

Upvotes: 4

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