解决 GNU 中的链接器错误以进行重新声明

Question

I have the following implementation:

header of A:

class A
{
public:
foo();
};

A has its own .cpp file with the implementation for foo()

//header of B

#include "A.h"
class B
{
public foo();
};

Note: B does not have a header of its own

Now in the Class C.cpp, I want to reuse header of A and implementation from Bo So in C.cpp I do:

//C.cpp
#include "A.h"
....
B b;
b.foo();
..

When I compile the above I am bound to get redeclaration error for the function foo(). I want to know if there is any way to tell GNU compiler to take Bo and omit Ao.. Or to tell compiler to consider the first object in the make file that contains the implementation and ignore the rest?

I am using GNU v2.16

Answer 1

Your problem is about redeclaration of A since in C.cpp it will see 2 declarations of A one through Ah and other through Bh , so just guard Ah in a header guard to avoid including it more than once, generally you should always guard your headers:

#ifndef HEADER_A_h_INCLUDED
#define HEADER_A_h_INCLUDED
class A {...};
#endif

Now if you include Ah more than one time this guard will make the second include as nothing!