CODEWITHSUNDEEP
c++c-preprocessorboost-preprocessor
Caduchon
Caduchon

Reputation: 5201

Preprocessor macro calling all possible combinations

I created a macro taking 3 conditions (as example, 8 in my real case):

#define FOO(A,B,C) \
  BOOST_PP_IF(A, a1, a2) \
  BOOST_PP_IF(B, b1, b2) \
  BOOST_PP_IF(C, c1, c2)

This works as I expect. Now I want to expand all the possibilities:

FOO(0,0,0)
FOO(0,0,1)
FOO(0,1,0)
FOO(0,1,1)
FOO(1,0,0)
FOO(1,0,1)
FOO(1,1,0)
FOO(1,1,1)

By this way, I have to write 8 lines. In my real case, I have to write 256 lines.

How can I generate it directly with (boost) preprocessor tools ?

MCV example with constructors declaration of a class Foo close to my real problem:

#define WRITE_FOO(A,B,C) \
  Foo(int a1 BOOST_PP_COMMA_IF(A) BOOST_PP_IF(A, int a2, BOOST_PP_EMPTY()),
           double b1 BOOST_PP_COMMA_IF(B) BOOST_PP_IF(B, double b2, BOOST_PP_EMPTY()),
           bool c1 BOOST_PP_COMMA_IF(C) BOOST_PP_IF(C, bool c2, BOOST_PP_EMPTY()));

Then

class Foo {
  public:
    WRITE_FOO(0,0,0)
    WRITE_FOO(0,0,1)
    WRITE_FOO(0,1,0)
    WRITE_FOO(0,1,1)
    WRITE_FOO(1,0,0)
    WRITE_FOO(1,0,1)
    WRITE_FOO(1,1,0)
    WRITE_FOO(1,1,1)
  private:
    int a_1;
    int a_2;
    double b_1;
    double b_2;
    bool c_1;
    bool c_2;
};

is extended to

class Foo {
  public:
    Foo(int a1, double b1, bool c1);
    Foo(int a1, double b1, bool c1, bool c2);
    Foo(int a1, double b1, double b2, bool c1);
    Foo(int a1, double b1, double b2, bool c1, bool c2);
    Foo(int a1, int a2, double b1, bool c1);
    Foo(int a1, int a2, double b1, bool c1, bool c2);
    Foo(int a1, int a2, double b1, double b2, bool c1);
    Foo(int a1, int a2, double b1, double b2, bool c1, bool c2);
  private:
    int a_1;
    int a_2;
    double b_1;
    double b_2;
    bool c_1;
    bool c_2;
};

The implementation is similar to:

#define IMPLEMENT_FOO(A,B,C) \
  Foo::Foo(int a1 BOOST_PP_COMMA_IF(A) BOOST_PP_IF(A, int a2, BOOST_PP_EMPTY()),
           double b1 BOOST_PP_COMMA_IF(B) BOOST_PP_IF(B, double b2, BOOST_PP_EMPTY()),
           bool c1 BOOST_PP_COMMA_IF(C) BOOST_PP_IF(C, bool c2, BOOST_PP_EMPTY())): \
    a_1(a1), \
    a_2(BOOST_PP_IF(A, a2, a1)), \
    b_1(b1),
    b_2(BOOST_PP_IF(B, b2, b1)), \
    c_1(c1),
    c_2(BOOST_PP_IF(C, c2, c1)) \
{}

Upvotes: 0

Views: 817

Answers (2)

user202729
user202729

Reputation: 3955

Not directly answer your question (this does not use macros), but you can solve your problem instead using template metaprogramming.

Unfortunately variadic template is a C++11 feature. This question contain more details about how to implement them for C++03 with pure C++, or this question with Boost.

Also requires linear code.

struct F{
    int i1,i2,d1,d2;

    template<class... Args>
    F(Args... args){init(args...);}

    void init(){} // base case
    template<class... Args>
    void init(int i1_,Args... args){i1=i1_;i2=i1_;init(args...);}
    template<class... Args>
    void init(int i1_,int i2_,Args... args){i1=i1_;i2=i2_;init(args...);}
    template<class... Args>
    void init(double d1_,Args... args){d1=d1_;d2=d1_;init(args...);}
    template<class... Args>
    void init(double d1_,double d2_,Args... args){d1=d1_;d2=d2_;init(args...);}

};

Try it online! (gcc) or Try it online! (clang)

Requires the types to be assignable. You may want to add some std::move if you're worried about efficiency.

Upvotes: 0

user202729
user202729

Reputation: 3955

This is a linear-code solution that solves the question (although I would not suggest doing that in real code, use templates instead if possible)

#define W2(...) W1(__VA_ARGS__,0) W1(__VA_ARGS__,1)
#define W1(...) W0(__VA_ARGS__,0) W0(__VA_ARGS__,1)
W2(0) W2(1)

Try it online!

Upvotes: 3

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