A little class problem

This is a class I'm using for a game I'm making and it is giving me these error;

Code:

---

C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|18|error: ISO C++ forbids initialization of member `x'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|18|error: making `x' static|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|18|error: ISO C++ forbids in-class initialization of non-const static member `x'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|19|error: ISO C++ forbids initialization of member `y'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|19|error: making `y' static|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|19|error: ISO C++ forbids in-class initialization of non-const static member `y'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|21|error: ISO C++ forbids initialization of member `right'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|21|error: making `right' static|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|21|error: ISO C++ forbids in-class initialization of non-const static member `right'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|22|error: ISO C++ forbids initialization of member `left'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|22|error: making `left' static|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|22|error: ISO C++ forbids in-class initialization of non-const static member `left'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|23|error: ISO C++ forbids initialization of member `up'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|23|error: making `up' static|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|23|error: ISO C++ forbids in-class initialization of non-const static member `up'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|24|error: ISO C++ forbids initialization of member `down'|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|24|error: making `down' static|
C:\Users\Bijan\Documents\C++ Programs\My SDL project\main.cpp|24|error: ISO C++ forbids in-class initialization of non-const static member `down'|
||=== Build finished: 18 errors, 2 warnings ===|

---

here is the class

Code:

---

class character{
    public:
    void handle_events();

    int x = 0;
    int y = 0;

    int right = 0;
    int left = 0;
    int up = 0;
    int down = 0;

    private:
    int collision_x();
    int collision_y();
};

---

The errors mean just what they say. You cannot give member objects a value in a class definition, since quite frankly they don't exist. They do not exist until an object of that class is constructed, and so this initialization is the job of the constructor.

Those values will all be initialized to 0 by default anyway (when an actual object is instantiated). If you want to initialize them to something else, use an initialization list:

Code:

---

class test {
        public:
                int x, y;
                test() : x(5), y(6) {}
};

---

Quote:

---

Originally Posted by MK27

Those values will all be initialized to 0 by default anyway (when an actual object is instantiated).

---

This is of course not true.

Code:

---

#include <iostream>
class test {
    public:
        int x;
};

int main() {
    test foo;
    std::cout << foo.x << std::endl;
    return 0;
}

---

Code:

---

$ ./a.out
3616756

---

Thanks you guys.

Quote:

---

Originally Posted by tabstop

This is of course not true.

---

Um:

Code:

---

using namespace std;

class test {
        public:
                int x, y;
                test() {}
};

int main() {
        test eg;

        cout << eg.x << eg.y;

        return 0;
}

---

00

Maybe a constructor is required or it is just g++, but I'm sure I've read the standard ensures this too. Lemme go consult BS...

Well, Barney has nothing to say, but I am most likely wrong here, this is just a g++ thing.

It may be a g++ thing but also can be a thing where compiling in release mode does nothing for variables and compiling in debug mode more often than not means that they are initialized to zero. Older compilers used to init them to all kinds of crazy values (oxDEADBEEF anyone?) in debug more but the less colorful 0 is the norm now.

Quote:

---

Originally Posted by MK27

Um:

Code:

---

using namespace std;

class test {
        public:
                int x, y;
                test() {}
};

int main() {
        test eg;

        cout << eg.x << eg.y;

        return 0;
}

---

00

Maybe a constructor is required or it is just g++, but I'm sure I've read the standard ensures this too. Lemme go consult BS...

---

And what did you think I was using?

Code:

---

andrewf@ubuntu:~$ cat >mk.cpp
#include <iostream>
using namespace std;

class test {
    public:
        int x, y;
        test() {}
};

int main() {
    test eg;
   
    cout << eg.x << eg.y;

    return 0;
}
andrewf@ubuntu:~$ g++ mk.cpp
andrewf@ubuntu:~$ ./a.out
134514368-1080144264

---

The tie-breaker (moi) goes to tabstop, though it does blow my debug mode theory. For:

Code:

---

class Foo
{
public:
  int x, y;
  Foo()
  {
      cout << "x,y in ctor: " << x << ", "<<  y << endl;
  }

};

---

in main.cpp, compiled on:

Code:

---

jeff@jeff-gate:~/dev/test1$ gcc --version
gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3
Copyright (C) 2009 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

jeff@jeff-gate:~/dev/test1$

---

With switches:

Code:

---

-Wall -ggdb

---

And called from main() like so:

Code:

---

int main(int argc, char *argv[])
{
  cout << "foo_test 1.0" << endl;
  Foo foo;
  cout << "Foo::x and Foo::y in main: " << foo.x << foo.y << endl;

---

Produces:

Code:

---

jeff@jeff-gate:~/dev/test1$ make clean && make
[ 50%] Building CXX object CMakeFiles/foo.dir/foo.cpp.o
Linking CXX shared library libfoo.so
[ 50%] Built target foo
[100%] Building CXX object CMakeFiles/foo_test.dir/foo_main.cpp.o
Linking CXX executable foo_test
[100%] Built target foo_test
jeff@jeff-gate:~/dev/test1$ ./foo_test
foo_test 1.0
x,y in ctor: 134524916, -1079089064
Foo::x and Foo::y in main: 134524916-1079089064

---

Hmmph.

Update:
Compiling with -O2 produced the additional compile output as well as the now more interesting program output:

Code:

---

jeff@jeff-gate:~/dev/test1$ make clean && make
-- Configuring done
-- Generating done
-- Build files have been written to: /home/jeff/dev/test1
[ 50%] Building CXX object CMakeFiles/foo.dir/foo.cpp.o
Linking CXX shared library libfoo.so
[ 50%] Built target foo
[100%] Building CXX object CMakeFiles/foo_test.dir/foo_main.cpp.o
/home/jeff/dev/test1/foo_main.cpp: In function ‘int main(int, char**)’:
/home/jeff/dev/test1/foo_main.cpp:21: warning: ‘foo.Foo::x’ may be used uninitialized in this function
/home/jeff/dev/test1/foo_main.cpp:36: note: ‘foo.Foo::x’ was declared here
/home/jeff/dev/test1/foo_main.cpp:21: warning: ‘foo.Foo::y’ may be used uninitialized in this function
/home/jeff/dev/test1/foo_main.cpp:36: note: ‘foo.Foo::y’ was declared here
Linking CXX executable foo_test
[100%] Built target foo_test
jeff@jeff-gate:~/dev/test1$ ./foo_test
foo_test 1.0
x,y in ctor: 0, 0
Foo::x and Foo::y in main: 00
Testing: foo
jeff@jeff-gate:~/dev/test1$

---

So there you have it.

I wasn't using any switches, gcc 4.3.2.

I guess the point is that I shouldn't count on that (time to go thru some code! ARGGGHH!). I could have sworn I read this was a standard thing somewhere.

Quote:

---

Originally Posted by MK27

I wasn't using any switches, gcc 4.3.2.

I guess the point is that I shouldn't count on that (time to go thru some code! ARGGGHH!). I could have sworn I read this was a standard thing somewhere.

---

It's supposed to default-construct each member of the class. But default-construct for int doesn't do a great deal.