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I want to implement a new max/min macro, which can take more than two parameter, for example:
#define max( ... ) ...
and then, I can use it like this:
max( p0, p1, p2, p3 )
max( 2, 4, 100 )
max( 1,2,3,4,5,6,7 ) -> 7
if this macro can help us to implement that macro?
#define PP_EXPAND(X) X
#define PP_ARG_COUNT(...) PP_EXPAND(PP_ARG_POPER(__VA_ARGS__, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0))
#define PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, N, ...) N
#define PP_ARG_AT(Index, ...) PP_ARG_AT_##Index(__VA_ARGS__)
#define PP_ARG_AT_0(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, __VA_ARGS__))
#define PP_ARG_AT_1(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, __VA_ARGS__))
#define PP_ARG_AT_2(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, __VA_ARGS__))
#define PP_ARG_AT_3(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, __VA_ARGS__))
#define PP_ARG_AT_4(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, __VA_ARGS__))
#define PP_ARG_AT_5(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, __VA_ARGS__))
#define PP_ARG_AT_6(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __VA_ARGS__))
#define PP_ARG_AT_7(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, _9, __VA_ARGS__))
#define PP_ARG_AT_8(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, _8, __VA_ARGS__))
#define PP_ARG_AT_9(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, _7, __VA_ARGS__))
#define PP_ARG_AT_10(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, _6, __VA_ARGS__))
#define PP_ARG_AT_11(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, _5, __VA_ARGS__))
#define PP_ARG_AT_12(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, _4, __VA_ARGS__))
#define PP_ARG_AT_13(...) PP_EXPAND(PP_ARG_POPER(_1, _2, _3, __VA_ARGS__))
#define PP_ARG_AT_14(...) PP_EXPAND(PP_ARG_POPER(_1, _2, __VA_ARGS__))
#define PP_ARG_AT_15(...) PP_EXPAND(PP_ARG_POPER(_1, __VA_ARGS__))
#define PP_ARG_AT_16(...) PP_EXPAND(PP_ARG_POPER( __VA_ARGS__))
722
For portability, you should not have more than 31 parameters for a macro. The parameter list may end with an ellipsis (…).
Yes. If you try untouchable(foo,first) you get an error because the macro only sees two parameters but was expecting 4.
The macro definition can include macro arguments, which can be assigned specific values in the macro call. There are two types of arguments: keyword and positional. Keyword arguments are assigned names in the macro definition; in the macro call, they are identified by name.
Except for functions with variable-length argument lists, the number of arguments in a function call must be the same as the number of parameters in the function definition. This number can be zero. The maximum number of arguments (and corresponding parameters) is 253 for a single function.
In C++11, std::max works with initializer_list, so you may use
std::max({40, 31, 42, 13, 4, 25, 16, 27});
And if you really want MAX(p1, p2, p3) syntax, you may do:
#define MAX(...) std::max({__VA_ARGS__})
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