CODEWITHSUNDEEP
c++
musako
musako

Reputation: 1267

How to use a function defined using a macro

I have defined the macro as follows


#define COMPARE(OPERATOR, FUNCTION)                                         \ 
    template <typename T>                                                   \
    void FUNCTION(T *compArrayA, T *compArrayB, bool *resArray, int size) { \
        for (int idx = 0; idx <= size; ++idx ) {                                  \
            resArray[idx] = (compArrayA[idx] OPERATOR compArrayB[idx]);  \
        }                                                                   \
    }                                                                       \

COMPARE(==, eq);
COMPARE(!=, nq);
COMPARE(>=, greater_eq);

So, I tried to call the function defined in the macro as follows.

float *ArrayA, *ArrayB;
bool *ArrayRes;

ArrayA = (float *) malloc(sizeof(float)* 100);
ArrayB = (float *) malloc(sizeof(float)* 100);
ArrayRes = (bool *) malloc(sizeof(bool) * 100);

eq(ArrayA, ArrayB, ArrayRes, 100);

I received the following error.

eq.h(11): error: expected an expression

1 error detected in the compilation of "eq.cpp".

eq.h(11) represents the following line.

COMPARE(==, eq);

How do I define a function in a macro?

I just want to know how to implement functions using macros.

Upvotes: 0

Views: 120

Answers (3)

Victor Gubin
Victor Gubin

Reputation: 2937

Short answer, don't do that. Since you've templates you can use standard library approach from functional header

without any macro definitions at all.

For example:

template<typename E, class Pred>                                                   
void vcompare(E *compArrayA, E *compArrayB, bool *resArray, int size) {
    for (int idx = 0; idx <= size; ++idx ) {                            
        resArray[idx] = Pred(compArrayA[idx], compArrayB[idx]);
    }                                                               
}

vcompare<int,std::less>(lhs,rhs,res,len);
vcompare<int,std::greater>(lhs,rhs,res,len);

P.S. Check std::vector class and general STL part inside standard C++ library.

Upvotes: 2

kingpin
kingpin

Reputation: 21

What you are trying to do is to pass operator as an argument.

Passing an operator as an argument to a function in C

As Victor Gubin already answered it is best to avoid macro and embrace modern alternatives to do the same you are trying to achieve.

Upvotes: 0

Jarod42
Jarod42

Reputation: 218268

As you define your MACRO, you shouldn't use ; after it, so

COMPARE(==, eq)
COMPARE(!=, nq)
COMPARE(>=, greater_eq)

instead of

COMPARE(==, eq);
COMPARE(!=, nq);
COMPARE(>=, greater_eq);

Upvotes: 1

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