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cat.hpp File Reference


Defines

#define BOOST_PREPROCESSOR_CAT(L, R)
 Delays the catenation of L and R. More...

Detailed Description

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Define Documentation

#define BOOST_PREPROCESSOR_CAT (  L,
R    ) 
 

Delays the catenation of L and R.

Example: 

  #define STATIC_ASSERT(EXPR)\
    enum\
    { BOOST_PREPROCESSOR_CAT(static_check_,__LINE__) = (EXPR) ? 1 : -1\
    };\
    typedef char\
      BOOST_PREPROCESSOR_CAT(static_assert_,__LINE__)\
      [ BOOST_PREPROCESSOR_CAT(static_check_,__LINE__)\
      ]

  // ...

  STATIC_ASSERT(sizeof(int) <= sizeof(long));

The above expands to: 

  enum
  { static_check_152 = (sizeof(int) <= sizeof(long)) ? 1 : -1
  };
  typedef char
    static_assert_152
    [ static_check_152
    ];

Using BOOST_PREPROCESSOR_CAT() above lets the preprocessor expand the __LINE__. If the above code would use the ## operator directly then __LINE__ would not be expanded and the above would expand to: 

  enum
  { static_check___LINE__ = (sizeof(int) <= sizeof(long)) ? 1 : -1
  };
  typedef char
    static_assert___LINE__
    [ static_check___LINE__
    ];

© Copyright Housemarque, Inc. 2001

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