About the method in the class

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The address of virtual method is stored in the vir_table in class.When we call a virtual method, we can search the vir_table in class to get that the method which we wanted.But the normal method is not stored in the vir_table.So, when we call a normal method by an object or a pointer.How do it know the normal method address?

Posted 9-Oct-12 15:43pm

okyanwenyi

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3 solutions

Solution 1

the normal method address gets assigned during the program compilation

Posted 9-Oct-12 16:46pm

chaau

Solution 2

C#

float (SomeClass::*my_memfunc_ptr)(int, char *);
// For const member functions, it's declared like this:
float (SomeClass::*my_const_memfunc_ptr)(int, char *) const;

   my_memfunc_ptr = &SomeClass::some_member_func;
 // This is the syntax for operators:
 my_memfunc_ptr = &SomeClass::operator !;

Member Function Pointers and the Fastest Possible C++ Delegates[^]

Posted 9-Oct-12 17:04pm

Santhosh G_

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pasztorpisti · Accepted Answer · 2012-10-09T21:27:00

A non-virtual method is just like a normal global function in this regard except that it accepts an extra hidden this pointer as its first parameter. The address of a non-virtual method is a fix location in your process address space.

This may be a stupid example but the following code:

C++

struct S
{
    int i;
    void f()
    {
        printf("%d\n", i);
    }
}

S s;
s.f();

...is basically compiled to something like this:

C++

struct S
{
    int i;
}

void f(S* _this_)
{
    printf("%d\n", _this_->i);
}

S s;
f(&s);

Knowing this reveals that there is no magic happening when you issue an s.f() method call. You just call the f() "function" residing in the S namespace by specifying an S instance as its first hidden parameter (that is &s in our case).

The only difference is that the readability of the code in the first block tends to be better (in my opinion - especially when the size of codebase increases) and there you can hide method f() from outer world by making it private and f() can see the private members of S (this is some kind of documentation and prevention of abuse - converting human coder mistakes into compile errors), the same isn't true for the second code block that is much like C code. I usually start to explain the beauty of C++ for C coders through a similar example on non-virtual methods. :-)