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From: cs00wsc@unccvax.UUCP (Shiang Chin)
Newsgroups: comp.lang.c++
Subject: C++ and SunView
Keywords: C++, SunView
Message-ID: <1804@unccvax.UUCP>
Date: 23 Jan 90 06:48:24 GMT
Distribution: usa
Organization: Univ. of NC at Charlotte, Charlotte, NC
Lines: 44

I have a problem when I create applications using
C++ and SunView. For example, If I define a class:

    Class A:
        private:
          int a;
        ...
        public:
          A();
          m1() { printf("%d\n",a);};
          ...
          ~A();
    };

and create a window with some command buttons by using SunView
library. I assigned the method 'a()' to one of the command
button as a called back notify procedure. 
Assumming the value stored in the variable 'a' now
is 100, when I clicked the mouse on that command button the
value printed out should be '100', but the value I
got was not correct. After many tries, I defined a global
variable:
     ...
     A* x;
     ....

and then redefined the class definition:

    Class A:
       private:
           int a;
           ...
       public:
          A() { x = this;};
          m1() {printf("%d\n",x->a);};
          ....
          ~A()
      }

Finally, I got the right value.
Does any one know why?
Thanx a lot.

Wen S. Chin at UNC Charlotte