C++ calls the wrong virtual function
Author
First, I would like to say sorry for not using a spell check, it's not working for some reason. Also, sorry for not giving a lot of detials, it's pretty stright forward.
I have a base class with a vritual function:
class BaseClass
{
public:
virtual void update(void) = 0;
};
now, I have 3 classes derived from BaseClass, and all with their own update() functions:
class Class1 : public BaseClass
{
public:
void update(void);
}
and the same for Class2 and Class3
Now when I do this:
BaseClass *testClass = new Class3();
and I call update:
testClass->update();
C++ should call the update() function that belonges to Class3. I know this and done it many times in many projects. The crazy thing is, C++ keeps calling the update() function that belonges to Class1 :/
The code is simple and straight forward. Does anyone know why something like this would happen??
Thanks.
I've never had this problem, but it could be an intellisense mishap. Try deleting the NCB and PDB files and rebuilding the solution. Also, make sure you are debugging in the Debug build.
Quote:
class Class1 : public BaseClass
{
public:
void update(void);
}
This is missing a semicolon on the end and thus won't compile. When diagnosing C++ code, please always paste your actual code. Really. I want to see the real source code for Class1 and Class3. It sounds like Class3 is supposed to inherit from Class1 or 2? If Class2, please post that as well.
Copy and paste. Don't introduce transcription errors.
I'm guessing your update function signatures aren't as uniform as you think they are. Please also copy and paste your test invocation code.
Also, when you do post the code indicated by MaulingMonkey you can maintain the formatting by placing it between [source] and [/source] tags, which will make it a whole lot easier to read aswell.
If your classes are in separate DLL's or something then it's because the you need to rebuild one or all of the projects so the interface is known across all. I've seen the problem quite often when the engineer forgets to rebuild either the client or the host library after adding, modifying, or removing an interface member function.
Of course, I have no idea how your project is structured, but that's when I've seen it.
Of course, I have no idea how your project is structured, but that's when I've seen it.
Just a shot in the dark:
If the code in the functions in question produced identical assembly when compiled and you are running a release build, then I wouldn't be surprised if it optimised out the extra functions that produced identical assembly and so in a release build it appeared to call the wrong one sometimes. I have seen this happen when debugging release builds! It is not a bug though, the program behaves as expected.
You still need to post the real code if it is a real problem.
If the code in the functions in question produced identical assembly when compiled and you are running a release build, then I wouldn't be surprised if it optimised out the extra functions that produced identical assembly and so in a release build it appeared to call the wrong one sometimes. I have seen this happen when debugging release builds! It is not a bug though, the program behaves as expected.
You still need to post the real code if it is a real problem.
Assuming Class3 inherits Class2, and Class2 inherits Class1; then "void update()" needs to be declared virtual in both the Class1 and Class2 declarations. Currently, update() is not virtual in Class1, so all pointers to Class1 and its parent classes have no way to dynamically link child implementations of update().
WhatsUnderThere, you are wrong. there is no way to make function not virtual if it was declared virtual somewhere before in base class
class A1
{
public:
virtual void foo() {cout<<"A1"<<endl;}
};
class A2 : public A1
{
public:
void foo() {cout<<"A2"<<endl;}
};
class A3 : public A2
{
public:
void foo() {cout<<"A3"<<endl;}
};
class A4 : public A3
{
public:
void foo() {cout<<"A4"<<endl;}
};
void main()
{
A1* p = new A4;
p->foo();
delete p;
}
the result output will be: A4
class A1
{
public:
virtual void foo() {cout<<"A1"<<endl;}
};
class A2 : public A1
{
public:
void foo() {cout<<"A2"<<endl;}
};
class A3 : public A2
{
public:
void foo() {cout<<"A3"<<endl;}
};
class A4 : public A3
{
public:
void foo() {cout<<"A4"<<endl;}
};
void main()
{
A1* p = new A4;
p->foo();
delete p;
}
the result output will be: A4
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