Re: Proposal for automatic generation of c++ header files

[David Brown]

On 12/01/2011 16:22, Achilleas Margaritis wrote:
Hello all.
I have a idea for automatic generation of headers in a c++ program.
Having to maintain headers is a very time consuming task, and I think
we will all benefit from such a thing. The idea is the following:

Each time the compiler finds the pragma

#pragma autoinclude("foo.hpp")

it does the following:

1) searches the include path for the header foo.hpp.

2) if the header does not exist, then the compiler searches for the
file 'foo.cpp'

3) if the file 'foo.cpp' is found, then the header 'foo.hpp' is
generated automatically from the the .cpp file.

4) if the header exists, then the compiler compares the file dates of
the header and the implementation files. If the header is older than
the implementation file, then a new header is generated from the
implementation file.

When the compiler finds a declaration in a .cpp file that is 100% the
same as a declaration in a header file, then the declaration in the
implementation file is ignored, because it has been created
automatically in the header by the compiler. If there is a difference,
then an error is declared.

Example:

file main.cpp:

#pragma autoinclude ("foo.hpp")

int main() {
     Foo *foo = new Foo;
     foo->bar();
     foos.push_back(foo);
}

file foo.cpp:

#include<list>

class Foo {
public:
     void bar() {
     }
};

std::list<Foo *>  foos;

static int data = 0;

The compiler generates the following header:

#ifndef FOO_HPP
#define FOO_HPP

#include<list>

class Foo {
public:
     void bar();
};

extern std::list<Foo *>  foos;

#endif //FOO_HPP

If such a feature existed, it would greatly speed up application
development for c++ applications.


I can see how such a feature could be useful, but is there any reason 
why it should be part of gcc, rather than a separate program that takes 
a cpp file and generates an hpp file?  Such a program would be much 
easier to develop and maintain than a new gcc pragma, and more flexible 
(for example, it could be used with other compilers).  Your timestamp 
checking features are easily accomplished with make.