Constants

Constants

Most libraries have some constant values that are required or make usage easier. In C code, this can be a #define or some const value. Most higher level languages handle constants in some way or another, and Wrapture cand translate the C code to fit.

Consider the following simple library, which sends a command to a VCR (man, remember those?) to perform a given action.

#define PLAY 1
#define PAUSE 2
#define FAST_FORWARD 3
#define REWIND 4
#define VOLUME_UP 5
#define VOLUME_DOWN 6

void send_command( struct vcr *target_vcr, int command );

Describing the class to include these constants is straightforward using the constants list, as shown below. The function description is left off, as there is nothing special about it (you can check the .yml file in this example to see the full specification)..

classes:
  - name: "VCR"
    namespace: "mediacenter"
    equivalent-struct:
      name: "vcr"
      includes:
        - "vcr.h"
    constants:
      - name: "PLAY_COMMAND"
        type: "int"
        value: "PLAY"
        includes:
          - "vcr.h"
      - name: "PAUSE_COMMAND"
        type: "int"
        value: "PAUSE"
      - name: "FAST_FORWARD_COMMAND"
        type: "int"
        value: "FAST_FORWARD"
      - name: "REWIND_COMMAND"
        type: "int"
        value: "REWIND"
      - name: "VOLUME_UP_COMMAND"
        type: "int"
        value: "VOLUME_UP"
      - name: "VOLUME_DOWN_COMMAND"
        type: "int"
        value: "VOLUME_DOWN"

Constants are given a name, type, and value which describe how they are defined in the wrapped language. The descriptions above will result in the following constant definitions inside of the C++ class:

namespace mediacenter {

  class VCR {
  public:

    static const int PLAY_COMMAND;
    static const int PAUSE_COMMAND;
    static const int FAST_FORWARD_COMMAND;
    static const int REWIND_COMMAND;
    static const int VOLUME_UP_COMMAND;
    static const int VOLUME_DOWN_COMMAND;

    // rest of class definition
  };
}

If you want to run this example, all that remains after using wrapture to generate the sources is to compile the various sources and run the vcr_usage program to see the output:

# assuming that you're using sh and have g++
g++ -I . vcr.c VCR.cpp vcr_usage.cpp -o vcr_usage_example
./vcr_usage_example