In C++ I made a funcion call as 4 threads.in that funcion there is an int value how can I use it in another function

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cv::VideoCapture a;
	cv::VideoCapture b;
	cv::VideoCapture c;
	cv::VideoCapture d;
	a.open("traffic1.mp4");
	b.open("traffic2.mp4");
	c.open("traffic3.mp4");
	d.open("traffic4.mp4");
	std::thread t1 (traffic,a,"a");
	std::thread t2 (traffic, b, "b");
	std::thread t3(traffic, c, "c");
	std::thread t4(traffic, d, "d");
	t1.join();
	t2.join();
	t3.join();
	t4.join();

here in function traffic() there is a integer value how can i access it what is the syntax

What I have tried:

i did't get any syntax for this

Posted 12-Mar-17 7:15am

abhiramthejas

Updated 13-Mar-17 0:39am

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Jochen Arndt 13-Mar-17 6:25am

How should we know?

You did not show us the traffic() function and the posted code did not contain any integer variable.

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KarstenK · Answer 1 · 2017-03-13T00:39:00

For use in other functions you must declare a global variable. You can use a normal int outside the traffic function.

But I would call it a major flaw that you have different threads accessing the same variable if the variable isnt constant for all threads .

It is not clear which thread wins the race for access. So it is better to write an getInteger() and setInteger() function with some syncronization code.

Please read the article C++11 threads, locks and condition variables for better understanding the pitfalls and solutions.