How do I output a compile-time numeric constant during compilation in Visual C++?

Question

Visual C++ has #pragma message that outputs a string into compiler output. Now I have a factory:

template
CComPtr          


        

Answer 1

If I understood your question correctly, then I think you can do this:

template 
struct overflow{ operator char() { return size + 256; } }; //always overflow
//if you doubt, you can use UCHAR_MAX +1 instead of 256, to ensure overflow.

template
CComPtr CreateComObject()
{
   CComPtr newObject( new CComObject );
   char(overflow)>());
   return newObject;
}

The value of sizeof(CComObject) will be printed as warning messages during compilation.

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See this small demo : http://www.ideone.com/Diiqy

Look at these messages (from the above link):

prog.cpp: In member function ‘overflow::operator char() [with unsigned int size = 4u]’:
prog.cpp: In member function ‘overflow::operator char() [with unsigned int size = 12u]’:
prog.cpp: In member function ‘overflow::operator char() [with unsigned int size = 400u]’:

In Visual Studio, you can see these messages in the Build Output tab; it may not appear in Error List > Warnings tab.

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The idea is taken from my another solution:

Calculating and printing factorial at compile time in C++