I have a code similar to this for the following array:
long int N = 424242424242; //random number
short int* spins = new short int spins[N];
std::fill(spins, spins N, 1);
Now let's suppose for some reason I want to add a couple of elements of that array into a short int called nn_sum:
short int nn_sum = spins[0] spins[1];
However, when I do this on CLion IDE, Clang-Tidy marks it yellow and tells me:
Clang-Tidy: Narrowing conversion from 'int' to signed type 'short' is implementation-defined
Why is this happening? Why is there any narrowing at all? Does C convert the shorts to ints when adding them? If so why, and is there something I can do to make it work better? Maybe even ditch the shorts entirely?
Keep in mind that I have code like this in a very computationally intensive part of the application so I want to make it as efficient as possible. Any other suggestion would also be appreciated.
CodePudding user response：
This happens because of integer promotion. The result of adding two short values is not short, but int.
You can check this with cppinsights.io:
short a = 1;
short b = 2;
auto c = a b; // c is int