C++: I have this config class that I want to use between all my CPP files, how do I initialize it?

Question

class Config
{
    public:

        static int OUTPUT_TO_FILE;
        static int NEED_TO_TRAIN;
        static int NO_FILE_TRAIN;
        static int NEED_TO_TEST;
}

Above is my header.h file (i followed: http://weblogs.asp.net/whaggard/archive/2004/11/05/252685.aspx)

and I want to be able to do things like Config.OUTPUT_TO_FILE = true or variable = Config.NO_FILE_TRAIN;

from any file that includes config.h

I have what I want to do is clear, Just want some variable shared throughout all my cpp files.

EDIT: I'm having trouble compiling:

In my make file, I added:

hPif : src/main.o src/fann_utils.o src/hashes.o src/config.o # added the config part
    g++ src/main.o src/fann_utils.o src/hashes.o src/config.o -lfann -L/usr/local/lib -o hPif

config.o : src/config.cpp src/config.h
    g++ -c src/config.cpp

.
.
.
main.o: src/main.cpp src/config.h src/main.h src/hashes.h
    g++ -c src/main.cpp

config.cpp:

#include "config.h"

int OUTPUT_TO_FILE = false;
.
.
.

config.h:

class Config
{
    public:

        static int OUTPUT_TO_FILE;
.
.
.

Trying to call by:

#include "config.h"
...

            Config::OUTPUT_TO_FILE = true;

Error I get:

Undefined Symbols:
  "Config::OUTPUT_TO_FILE", referenced from:
      _main in main.o
      _main in main.o

possible duplicate of [C++ Initialize class static data member](http://stackoverflow.com/questions/4192008/c-initialize-class-static-data-member) — Hans Passant, Apr 01 '11 at 14:18
@Beta: on many systems there is no `bool`. If want use platform independent code without many defines, easier to use other type than `bool`. — Naszta, Apr 01 '11 at 14:31
Where did you try it? `Config::OUTPUT_TO_FILE = true;` If in main.cpp you should add `#include "Config.h"`. — Naszta, Apr 01 '11 at 15:04

Naszta · Accepted Answer · 2011-04-01T14:57:08.797

8

Header (Config.h):

#pragma once

class Config
{
public:
  static int OUTPUT_TO_FILE;
  static int NEED_TO_TRAIN;
  static int NO_FILE_TRAIN;
  static int NEED_TO_TEST;
};

Source (Config.cpp):

#include "Config.h"

int Config::OUTPUT_TO_FILE = 0;
int Config::NEED_TO_TRAIN = 0;
int Config::NO_FILE_TRAIN = 0;
int Config::NEED_TO_TEST = 0;

Usage (any.cpp):

#include "Config.h"

...
int variable = Config::OUTPUT_TO_FILE;
...

edited Apr 01 '11 at 14:57

answered Apr 01 '11 at 14:18

Naszta

7,560
2
33
49

Adding somedetails, as I am having trouble compiling. – NullVoxPopuli Apr 01 '11 at 14:55
@DerNalia: Config.h and Config.cpp are ready and fully detailed. – Naszta Apr 01 '11 at 14:58
I think the problem may have my case... should be Config.h, not config.h – NullVoxPopuli Apr 01 '11 at 15:09
@DerNalia: Yes, in un*x match case is important. – Naszta Apr 01 '11 at 15:17

score 0 · Answer 2 · answered Apr 01 '11 at 14:18

0

In one of your source files, add something like this:

int Config::OUTPUT_TO_FILE = 1;

Now, it will be initialized on program startup. Only do this in one source .cpp file, not in multiple.

answered Apr 01 '11 at 14:18

Thalur

1,155
9
13

score 0 · Answer 3 · answered Apr 01 '11 at 14:18

Because the class only has statics, you should be able to access them in any file which includes this header, for example..

foo.cpp

#include "Config.h"

void bar()
{
  Config::NO_FILE_TRAIN = 0; // set this value for example
}

bar.cpp

#include "Config.h"

void foo()
{
  Config::NEED_TO_TRAIN = 1; // set this value for example
}

Remember you must have an implementation file that is also compiled which actually defines the statics, i.e.

Config.cpp

int Config::OUTPUT_TO_FILE = 0; // initial value
:  //etc.

Adding some details, as I am having trouble compiling. – NullVoxPopuli Apr 01 '11 at 14:55 — NullVoxPopuli, Apr 01 '11 at 14:55

score 0 · Answer 4 · answered Apr 01 '11 at 14:22

0

You might want to implement your Config class as a singleton.

Oh, and if you want to set OUTPUT_TO_FILE = true, you'd be better off declaring OUTPUT_TO_FILE as bool...

answered Apr 01 '11 at 14:22

Christian Severin

1,793
19
38

C++: I have this config class that I want to use between all my CPP files, how do I initialize it?

4 Answers4

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