CODEWITHSUNDEEP
c++conditional-compilation
hertzsprung
hertzsprung

Reputation: 9893

C++ conditional compilation for a class with an optional dependency

I have a Rainfall class whose implementation depends on NetCDF, but the project should be compilable with or without NetCDF. Can I achieve conditional compilation without sprinkling preprocessor directives all over the code? What's the best practice in this situation?

rainfall.hpp

#pragma once

class Rainfall {
public:
    // several constructors, methods, and destructor
private:
    // several methods and variables
};

rainfall.cpp

#include "rainfall.hpp"
#include <netcdf.h>

// concrete implementation of class members

main.cpp

#include "rainfall.hpp"
#include <stdio>
#include <cstdlib>

void main_loop();

int main(int argc, char* argv[]) {
    if (user_wants_rainfall) {
#ifndef NETCDF
        std::cerr << "Rainfall not available: project was not compiled with NetCDF\n";
        return EXIT_FAILURE;
#endif
    }

    main_loop();

    return EXIT_SUCCESS;
}

void main_loop() {
    Rainfall rainfall;
    while (t < end_time) {
        if (user_wants_rainfall) rainfall.apply_to_simulation();
        t++;
    }
}

Upvotes: 1

Views: 676

Answers (1)

Gentil-N
Gentil-N

Reputation: 124

If you want a project that can be compiled with or without a specified library, you need to have two implementations

rainfall_netcdf.cpp

#ifdef USE_NETCDF
#include "rainfall.hpp"
#include <netcdf.h>
//your definitions using your lib
#endif //USE_NETCDF

rainfall.cpp

#ifndef USE_NETCDF
#include "rainfall.hpp"
//your definitions without your lib
#endif //USE_NETCDF

And in your project, you must define the USE_NETCDF macro if you want to use this lib. For example in visual studio : >properties >C/C++ >Preprocessor >Preprocessor definitions.

Upvotes: 1

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