CODEWITHSUNDEEP
c++functionscopemember
capricorn_heitus
capricorn_heitus

Reputation: 73

Calling member functions of a class before class declaration

I am defining a macro before a class declaration. The macro calls a member function of the class. My sample code is below.

Sample class declaration,

// sample.h

#include <sstream>
#include <iostream>
using namespace std;

#define CALCULATETEMP(a, b, c) {
int d = Sample::getTempIncrement(a,b,c);
stringstream ss;
ss << d;
cout << ss.str() << endl;
}

class Sample {
public:
    Sample();
    int getTempIncrement(int a, int b, int c);
    ~Sample();
};

Sample class implementation,

//sample.cpp

#include "sample.h"
Sample::Sample() {
}

int Sample::getTempIncrement(int a, int b, int c) {
    int temp = 5;
    int d = (a*temp) + (b+c)*temp;
    return d;
}

Sample::~Sample() {
}

Main routine,

//main.cpp

#include "sample.h"

int main(int argc, char* argv[]) {
    int a = 1;
    int b = 2;
    int c = 3;
    CALCULATETEMP(a, b, c);
    return 0;
}

When I run the main.cpp, I am getting an error in sample.h file within the macro definition: "Sample" is not a class or namespace name.

How can I call a member function of the class outside the scope of the class and before the class declaration? I am quite new to programming, your feedback would help me, Thanks.

Upvotes: 2

Views: 1225

Answers (3)

user888379
user888379

Reputation: 1467

I believe there's another problem, as well. Sample::getTempIncrement() isn't declared as a static, so you'll need a Sample instance available in the macro.

Upvotes: 2

Edward Strange
Edward Strange

Reputation: 40859

You've defined CALCULATETEMP(a,b,c) to be replaced by the preprocessor with { and then followed it with a bunch of global space coding, which is quite illegal.

I would suggest going back to the tutorial on preprocessor macros and/or reading up on inline functions.

Upvotes: 0

Seth Carnegie
Seth Carnegie

Reputation: 75130

If you want a macro to span multiple lines, you have to put \ at the end of each line:

#define CALCULATETEMP(a, b, c) {         \
int d = Sample::getTempIncrement(a,b,c); \
stringstream ss;                         \
ss << d;                                 \
cout << ss.str() << endl;                \
}

Also, why don't you just use a function for this (and not use stringstream)?

class Sample {
public:
    Sample();
    int getTempIncrement(int a, int b, int c);
    ~Sample();
};

void calctemp(int a, int b, int c) {
    int d = Sample::getTempIncrement(a,b,c);
    stringstream ss;
    ss << d;
    cout << ss.str() << endl; // why are you using stringstream? It could be
                              // just cout << d << endl;
}

Upvotes: 4

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