Should C++ eliminate header files? [closed]

Answer 1

Header files are an integral part of the language. Without header files, all static libraries, dynamic libraries, pretty much any pre-compiled library becomes useless. Header files also make it easier to document everything, and make it possible to look over a library/file's API without going over every single bit of code.

They also make it easier to organize your program. Yes, you have to be constantly switching from source to header, but they also allow you define internal and private APIs inside the implementations. For example:

MySource.h:

extern int my_library_entry_point(int api_to_use, ...);

MySource.c:

int private_function_that_CANNOT_be_public();

int my_library_entry_point(int api_to_use, ...){
  // [...] Do stuff
}

int private_function_that_CANNOT_be_public() {

}

If you #include <MySource.h>, then you get my_library_entry_point.

If you #include <MySource.c>, then you also get private_function_that_CANNOT_be_public.

You see how that could be a very bad thing if you had a function to get a list of passwords, or a function which implemented your encryption algorithm, or a function that would expose the internals of an OS, or a function that overrode privileges, etc.

Answer 2

Oh Yes!

After coding in Java and C# it's really annoying to have 2 files for every classes. So I was thinking how can I merge them without breaking existing code.

In fact, it's really easy. Just put the definition (implementation) inside an #ifdef section and add a define on the compiler command line to compile that file. That's it.

Here is an example:

/* File ClassA.cpp */

#ifndef _ClassA_
#define _ClassA_

#include "ClassB.cpp"
#include "InterfaceC.cpp"

class ClassA : public InterfaceC
{
public:
    ClassA(void);
    virtual ~ClassA(void);

    virtual void methodC();

private:
    ClassB b;
};

#endif

#ifdef compiling_ClassA

ClassA::ClassA(void)
{
}

ClassA::~ClassA(void)
{
}

void ClassA::methodC()
{
}

#endif

On the command line, compile that file with

-D compiling_ClassA

The other files that need to include ClassA can just do

#include "ClassA.cpp"

Of course the addition of the define on the command line can easily be added with a macro expansion (Visual Studio compiler) or with an automatic variables (gnu make) and using the same nomenclature for the define name.

Answer 3

Still I don't get the point of some statements. Separation of API and implementation is a very good thing, but header files are not API. There are private fields there. If you add or remove private field you change implementation and not API.

Answer 4

Backwards Compatibility - Header files are not eliminated because it would break Backwards Compatibility.

Answer 5

One of C++'s goals is to be a superset of C, and it's difficult for it to do so if it cannot support header files. And, by extension, if you wish to excise header files you may as well consider excising CPP (the pre-processor, not plus-plus) altogether; both C# and Java do not specify macro pre-processors with their standards (but it should be noted in some cases they can be and even are used even with these languages).

As C++ is designed right now, you need prototypes -- just as in C -- to statically check any compiled code that references external functions and classes. Without header files, you would have to type out these class definitions and function declarations prior to using them. For C++ not to use header files, you'd have to add a feature in the language that would support something like Java's import keyword. That'd be a major addition, and change; to answer your question of if it'd be practical: I don't think so--not at all.