Dynamic variable type definition

[baxy]

Hi,

Question: Is there a way do dynamically define a variable?

Example:

given a number i decide will my next number be defined as 16, 32 or 64 bit integer.

in c i can do that with helper functions and macros. I probably can do the same thing here in c++, but is there maybe an alternative c++ way?

int a = 300;

if a> 255

  // b should be defined as 32 bit integer

if a > 2^32

  // b should be defined as 64 bit integer

// initialize b 

// then pass this b into some function template that can handle 32 and 64 bit integers

thank you

baxy

[C_ntua]

The standard way is a union

union integerX
{
    int16 i16;
    int32 i32;
    int64 i64;
};

You can look here

You allocate memory as the biggest member, so 64 bits. If you want to save memory there are other workarounds but I guess your intent is just to have the correct type.

[King Mir]

yes, provided that a is a constant.

//untested, may have typos
#include <type_traits>

enum{
  DETERMINING_QUANTITY = 300
}

typedef std::conditional<  DETERMINING_QUANTITY < 4294967296ll, int, long long>::type ConditionalType;

ConditionalType conditionally_typed_variable;

void foo(int x);

void foo(long long x);

int main(){
  //this calls the right version of foo
  foo(conditionally_typed_variable);
}

EDIT: If a is not a constant, then something like this may work:

void foo(int x);

void foo(long long x);


int main(){
  int determining_quantity = 300;
  long long determining_variable;
  if(determining_quantity <4294967296ll )
    foo(static_cast<int>(determining_variable));
  else
    foo(determining_variable);
}

[iMalc]

It would be great if you would show us how you do it in C as it would leave no doubt as to what you actually want to do.