Ensures() - guideline support library

Question

I am trying to understand how to use Ensures() in code. As given in the example, if I tried using Ensures() as follows...

int main(void)
{
    int result = 0;
    // Some calculation
    Ensures(result == 255);
    return 0;
}

If the result variable is not equal to 255, the program crashes with the following output "terminate called without an active exception". My question is how to use Ensures() properly?

Answer 1

Are you using the Microsoft GSL implementation? Then if you check the gsl_assert.h header file you will see that if GSL_TERMINATE_ON_CONTRACT_VIOLATION is defined (which is default) then Ensures will call std::terminate which will give you the error you get.

If you want an exception to be thrown (with file and line-number information) then you need to define GSL_THROW_ON_CONTRACT_VIOLATION before including the GSL.

As for if you're using Ensures properly, then yes you are.

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Updates on 2021

GSL_TERMINATE_ON_CONTRACT_VIOLATION is removed, always calling terminate().