Conference turris::c_plus_plus

3494.0. "Assigment operator and array" by TAEC::GERVAIS () Mon Mar 17 1997 04:19

compiler :  DEC C++ V5.4-006 on Digital UNIX (Alpha)

Hello,

	I defined a class managing an array, but the compiler does not
	recognize the assignment operator with an array.
	
	Could you help me.

	Best Regards,

		Christophe.
	
Program:
--------

typedef char T_ARRAY[10];

class CTestArray
{
  T_ARRAY value;

public:

  CTestArray() {};

  CTestArray(const T_ARRAY& v)
  {
    memcpy(&value,&v,sizeof(T_ARRAY));
  }

  CTestArray& operator = (const T_ARRAY& v)
  { 
    memcpy(&value,&v,sizeof(T_ARRAY));
    return *this;
  }
};

void main()
{
  T_ARRAY val1= {1,2,3,4,5,6,7,8,9,10};
  T_ARRAY val2= {10,20,30,40,50,60,70,80,90,100};
  CTestArray foo(val1);

  foo=val2;
}
	 

Compilation result:
-------------------
>cxx -w0 -o test_array test_array.cxx
cxx: Error: test_array.cxx, line 30: In this statement, the argument list "foo=v
al2" matches no "CTestArray::operator =".
  foo=val2;
--^
cxx: Info: test_array.cxx, line 30: In this statement, tried to match "CTestArra
y::operator =" with the type "function (reference to const array [10] of char) r
eturning reference to CTestArray" declared at line number 17 in file test_array.
cxx.
  foo=val2;
--^
cxx: Info: test_array.cxx, line 30: In this statement, tried to match "CTestArra
y::operator =" with the type "function (reference to const CTestArray) returning
 reference to CTestArray" declared at line number 4 in file test_array.cxx.
  foo=val2;
--^

I think your program should compile, but the
compiler has a bug in it.

For now, you can workaround it by changing your
op= declaration to use a non-ref arg:

#ifdef __DECCXX // workaround cxx bug
  CTestArray& operator = (const T_ARRAY v)
#else
  CTestArray& operator = (const T_ARRAY& v)
#endif

Also, I would suggest making T_ARRAY a public
typedef of class CTestArray instead of a global.

I will enter this bug in our internal bugs database.

Hello,

	Do you know in which relaease of DECCXX the
	bug will be fixed ??


	Thanks you,

	Christophe.
	

This is fixed in V6.0.  Is there a problem in using
the workaround in the meantime?

	Hello,

	I redefined the assignment operator of the class using your
	workaround and it works.

	Regards,

		Christophe

	class CTestArray
	{
  	T_ARRAY value;

	public:

  	CTestArray() {};

  	CTestArray(const T_ARRAY& v)
  	{
    	memcpy(&value,&v,sizeof(T_ARRAY));
  	}

  	CTestArray& operator = (const T_ARRAY v)
  	{ 
    	memcpy(&value,v,sizeof(T_ARRAY));
    	return *this;
  	}
	};

Thanks for the feedback.