如何在Visual C ++中编译期间输出编译时数字常量？ [英] How do I output a compile-time numeric constant during compilation in Visual C++?

问题描述

Visual C ++有 #pragma message 表示将字符串输出到编译器输出。现在我有一个工厂：

  template< class Type> 
 CComPtr< Type> CreateComObject（）
 {
 CComPtr< Type> newObject（new CComObject< Type>）; 
 //做一些调整对象
 return newObject; 
} 
  

，我想输出传递给 new （即 sizeof（CComObject< Type>））看起来像 #pragma message 只接受字符串。

如何输出编译时数字常量？

解决方案

如果我正确理解你的问题，我想你可以这样做：

 模板< size_t size> 
 struct overflow {operator char（）{return size + 256;}}; //总是溢出
 //如果你怀疑，可以使用UCHAR_MAX +1而不是256，确保溢出
 
 template< class Type> 
 CComPtr< Type> CreateComObject（）
 {
 CComPtr< Type> newObject（new CComObject< Type>）; 
 char（overflow< sizeof（CComObject< Type>）>（））; 
 return newObject; 
} 
  
 
 
  sizeof（CComObject< Type>）的值将在编译期间作为警告消息打印。
 
 
 
 
 
 
查看此小演示： http：//www.ideone。 com / Diiqy  
 
 
 
查看以下讯息（来自上述连结）：
 
 
 prog.cpp：在成员函数
'overflow :: operator char（）[with 
 unsigned int  size = 4u ]'：
 
 prog.cpp：In 
成员函数
'overflow :: operator char（）[with 
 unsigned int  size = 12u ]'：
 
 prog.cpp：
在成员函数
'overflow :: operator char（）[with 
 unsigned int  size = 400u ]'：
 
 
在Visual Studio中，您可以在构建输出选项卡中看到这些消息;它可能不会出现在错误列表>警告标签中。
 
 
 
 
 
 
另一个解决方案：
 
 
 
 在C ++中在编译时计算和打印阶乘  
 
Visual C++ has #pragma message that outputs a string into compiler output. Now I have a factory:
template<class Type>
CComPtr<Type> CreateComObject()
{
   CComPtr<Type> newObject( new CComObject<Type> );
   //do some tuning to the object
   return newObject;
}
and I want to output the size of class that is passed to new (namely sizeof( CComObject<Type> ) into the compiler output. Looks like #pragma message only accepts strings.

How can I output a compile-time numeric constant?
解决方案
If I understood your question correctly, then I think you can do this:
template<size_t size> 
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<class Type>
CComPtr<Type> CreateComObject()
{
   CComPtr<Type> newObject( new CComObject<Type> );
   char(overflow<sizeof(CComObject<Type>)>());
   return newObject;
}
The value of sizeof(CComObject<Type>) will be printed as warning messages during compilation.



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.



The idea is taken from my another solution:

Calculating and printing factorial at compile time in C++

                        
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