Will the code compile now? If so, predict the output and explain.

Question

The following program has been partitioned into two files. Before we commented out the keyword namespace and the curly braces that were around func(int) this program compiled and had this output:
func(5) = 25
junk(5) = 75
```
// This goes in file A.cpp
//namespace //
//{
int func(int i)
{
return i*3;
}
//}
int junk (int i)
{
return i*func(i);
}

// This goes in file B.cpp
#include
int func(int i)
{
return i*5;
}
int junk(int i); //from A.cpp
int main()
{
cout <<”func(5) = “ << func(5) << endl;
cout <<”junk(5) = “ << junk(5) << endl;
}
```

Answer 1

Compilers compliant with the Standard in this respect will say that func(int) is multiply defined. Inexplicably, one compiler links to the version of func(int) from file A.cpp for all calls to func(5).
Explanation: C++ does not allow two definitions for any object to be visible in any namespace. Both the definition of func(int) in file A.cpp and the definition of func(int) in B.cpp are both in the global namespace, hence together are illegal. (VC++6.0, which is packed with the text, and the GNU C++ compilers, g++-2.9.5 and g++-3.0 give the error message: “multiply defined function func(int)”. The Borland command line compiler BCC 5.5 compiles the program, ignores the multiply defined function, and links to the version of func(int) from file A.cpp.)