c++ Threads inside for loop print wrong values

Question

I\'m trying to understand Multi-threading in c++, but I\'am stuck in this problem: if I launch threads in a for loop they print wrong values. This is the code:

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Answer 1

Two problems:

1. You have no control over when the thread runs, which means the value of the variable i in the lambda might not be what you expect.

2. The variable i is local for the loop and the loop only. If the loop finishes before one or more thread runs, those threads will have an invalid reference to a variable whose lifetime have ended.

You can solve both these problems very simply by capturing the variable i by value instead of by reference. That means each thread will have a copy of the value, and that copy will be made uniquely for each thread.