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c++sizeoftype-promotion

The standard way to get sizeof(promoted(x))

Is there a standard way to get the size of the type a variable would be promoted to when passed as a variadic argument?

auto x = ...;
auto y = sizeof(promoted(x));

The results should be:

char  -> sizeof(int)
int   -> sizeof(int)
float -> sizeof(double)
...
Solution

  • We can simply declare overloaded promoted functions with the proper types:

    int promoted(char);
int promoted(short);
int promoted(int);
long promoted(long);
long long promoted(long long);
double promoted(float);
double promoted(double);
long double promoted(long double);

    Note that the functions need no implementations, because we are never actually calling them.

    Here is a simple test run which prints 1, 4 and 4, 8 on my machine:

    std::cout << sizeof('a') << '\n';
std::cout << sizeof(promoted('a')) << '\n';

std::cout << sizeof(3.14f) << '\n';
std::cout << sizeof(promoted(3.14f)) << '\n';