virtual function

[hugheslin]

Hi,

Please consider the following classes:

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class Shape
{
......
......
public:
virtual void draw(CDC & aDC, COLORREF color, COLORREF fcolor, int
width, BOOL Filled = false) = 0;
};

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class Line : public Shape
{
......
......
public:
void draw(CDC &dc, COLORREF color, COLORREF fcolor, int width,
BOOL Filled = false);
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class ellipse : public Shape
{
......
......
public:
void draw(CDC & dc, COLORREF color, COLORREF fcolor, int width,
BOOL Filled = false);
};
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

My question is:

If I declared the member function "draw( )" inside the classes and
implemented the definitions of "draw( )" outside the classes, then
there will be an error messsage when compiling :

"redefinition of default parameter : parameter 5"

However, if I implemented all the definitions of "draw( )" inside the
classes, then the code can pass the compilation.

Would anybody please let me know what the issue is? Thakns a lot.

[Gavin Deane]

hu*******@hotmail.com wrote:

Hi,

Please consider the following classes:

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class Shape
{
.....
.....
public:
virtual void draw(CDC & aDC, COLORREF color, COLORREF fcolor, int
width, BOOL Filled = false) = 0;
};

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class Line : public Shape
{
.....
.....
public:
void draw(CDC &dc, COLORREF color, COLORREF fcolor, int width,
BOOL Filled = false);
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class ellipse : public Shape
{
.....
.....
public:
void draw(CDC & dc, COLORREF color, COLORREF fcolor, int width,
BOOL Filled = false);
};
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

My question is:

If I declared the member function "draw( )" inside the classes and
implemented the definitions of "draw( )" outside the classes, then
there will be an error messsage when compiling :

"redefinition of default parameter : parameter 5"

However, if I implemented all the definitions of "draw( )" inside the
classes, then the code can pass the compilation.

A much simpler example of the same problem is the following

// Function declaration
void foo(int i = 42);

int main()
{
return 0;
}

// Function definition
void foo(int i = 42) {}

You are not allowed to define the default parameter in two places. The
solution is either

// Function declaration and definition
void foo(int i = 42) {}

int main()
{
return 0;
}

which is the equivalent of you defining your draw functions inside your
classes, or

// Function declaration
void foo(int i = 42) {}

int main()
{
return 0;
}

// Function definition
// Note default parameter not redefined
void foo(int i) {}

Gavin Deane

[Neelesh Bodas]

hu*******@hotmail.com wrote:

Hi,

Please consider the following classes:
class Shape {> public: virtual void draw(CDC & aDC, COLORREF color, COLORREF fcolor, int
width, BOOL Filled = false) = 0;
};
class Line : public Shape
{
public:
void draw(CDC &dc, COLORREF color, COLORREF fcolor, int width,
BOOL Filled = false);
} My question is:

If I declared the member function "draw( )" inside the classes and
implemented the definitions of "draw( )" outside the classes, then
there will be an error messsage when compiling :

"redefinition of default parameter : parameter 5"

Actually, your question has nothing to with "virtual functions". C++
doesnot allow redefinition of default arguments of functions. So once
they are defined in the function prototype, you should not specify them
again in the function definition.
<quote>
8.3.6p4 : A default argument shall not be redefined by a later
declaration (not even to the same value).
</quote>

[Fiesta]

Hi Gavin,

Thanks a lot for your suggestion and it did help. Thanks again.
Gavin Deane wrote:

Hi,

Please consider the following classes:

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class Shape
{
.....
.....
public:
virtual void draw(CDC & aDC, COLORREF color, COLORREF fcolor, int
width, BOOL Filled = false) = 0;
};

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class Line : public Shape
{
.....
.....
public:
void draw(CDC &dc, COLORREF color, COLORREF fcolor, int width,
BOOL Filled = false);
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
class ellipse : public Shape
{
.....
.....
public:
void draw(CDC & dc, COLORREF color, COLORREF fcolor, int width,
BOOL Filled = false);
};
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

My question is:

If I declared the member function "draw( )" inside the classes and
implemented the definitions of "draw( )" outside the classes, then
there will be an error messsage when compiling :

"redefinition of default parameter : parameter 5"

However, if I implemented all the definitions of "draw( )" inside the
classes, then the code can pass the compilation.

A much simpler example of the same problem is the following

// Function declaration
void foo(int i = 42);

int main()
{
return 0;
}

// Function definition
void foo(int i = 42) {}

You are not allowed to define the default parameter in two places. The
solution is either

// Function declaration and definition
void foo(int i = 42) {}

int main()
{
return 0;
}

which is the equivalent of you defining your draw functions inside your
classes, or

// Function declaration
void foo(int i = 42) {}

int main()
{
return 0;
}

// Function definition
// Note default parameter not redefined
void foo(int i) {}

Gavin Deane