Global Functions(Newbee Q)

[joninty]

Hi,
I'm getting an error that a global function cannot be called from within a class. How do I ensure that this class has acess to all gobal fuctions.
The global function is in a .cpp

[Plastelin]

Imposible, Global function are always avalible from Members, or from other global functions, may be you cpp did not know name of this function because you do not declare it purpoly:

// .h file
void MyFn(int);

// .cpp file
void MyFn(int iID)
{
// ToDo somethink
}

[joninty]

Well I dont declare the global fuction in the header, but does this make a difference?
For example if I had a main.cpp with a bunch of globals and no corresponding main.h couldnt I still acess all the global functions.
Anyway the global function are in a .cpp and are just defined as normal.

returntype functionName(parameters)
{
//function body
}

[Elrond]

As said, to access your global function, the class needs to know it. You do it by either defining the function in the same .cpp as the class and access it from the members of the class that are defined in that same .cpp, OR you define all your global functions in a .h file and implement them in a .cpp file and then include this .h file in your class header file.

the example given by Plastelin seemed good.

[Sturmritter]

Use a "this->" pointer for global functions within a class.

It is not applicable in all cases though. Check the help files by doing an index search under "this" and select C++ library entry.


"The this pointer is a pointer accessible only within the nonstatic member functions of a class, struct, or union type. It points to the object for which the member function is called. Static member functions do not have a this pointer.

this
this->member-identifier
An object's this pointer is not part of the object itself; it is not reflected in the result of a sizeof statement on the object. Instead, when a nonstatic member function is called for an object, the address of the object is passed by the compiler as a hidden argument to the function. For example, the following function call:

myDate.setMonth( 3 );
can be interpreted this way:

setMonth( &myDate, 3 );
The object's address is available from within the member function as the this pointer. Most uses of this are implicit. It is legal, though unnecessary, to explicitly use this when referring to members of the class. For example:

void Date::setMonth( int mn ) {
month = mn; // These three statements
this->month = mn; // are equivalent
(*this).month = mn;
}
The expression *this is commonly used to return the current object from a member function:

return *this;
The this pointer is also used to guard against self-reference:

if (&Object != this) {
// do not execute in cases of self-reference
Note Because the this pointer is nonmodifiable, assignments to this are not allowed. Earlier implementations of C++ allowed assignments to this.
Occasionally, the this pointer is used directly — for example, to manipulate self-referential data structures, where the address of the current object is required.

Example
// this_pointer.cpp
// compile with: /EHsc
#include <iostream>
#include <string.h>

using namespace std;

class Buf {
public:
Buf( char* s );
Buf& operator=( const Buf & );
void Display() { cout << buffer << endl; }
private:
char* buffer;
};

Buf::Buf( char* s ) {
buffer = new char[ strlen( s ) + 1 ];
strcpy( buffer, s );
}
Buf& Buf::operator=( const Buf &otherbuf ) {
if( &otherbuf != this ) {
delete [] buffer;
buffer = new char[ strlen( otherbuf.buffer ) + 1 ];
strcpy( buffer, otherbuf.buffer );
}
return *this;
}
void main() {
Buf myBuf( "my buffer" );
Buf yourBuf( "your buffer" );
myBuf.Display();
myBuf = yourBuf;
myBuf.Display();
}
From Microsoft SDK help file


Hope that helps.

- Sturmritter