CODEWITHSUNDEEP
c++macrosc-preprocessor
Hank
Hank

Reputation: 527

How can I write "#include" only once?

In some large C++ projects, there are many #include directives. For example,

#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

I have to write four #include in this example. I am so lazy that I only want to write it once. Perhaps like this:

#include {
    <iostream>
    <boost/asio.hpp>
    <boost/bind.hpp>
    <boost/date_time/posix_time/posix_time.hpp>
}

Is there any way to do it like this? Or can we define a macro to do this?

Upvotes: 1

Views: 1180

Answers (5)

ilent2
ilent2

Reputation: 5241

Here is a macro that you could use (I wouldn't want to though, it made a nice little exercise on writing macros though):

#define HASH #
#define F(X) X

#define INCLUDE(X) F(HASH)include <X>

#define FEI_1(X, ...) INCLUDE(X)
#define FEI_2(X, ...) INCLUDE(X) NEW_LINE FEI_1(__VA_ARGS__)
#define FEI_3(X, ...) INCLUDE(X) NEW_LINE FEI_2(__VA_ARGS__)
#define FEI_4(X, ...) INCLUDE(X) NEW_LINE FEI_3(__VA_ARGS__)
#define FEI_5(X, ...) INCLUDE(X) NEW_LINE FEI_4(__VA_ARGS__)
#define FEI_6(X, ...) INCLUDE(X) NEW_LINE FEI_5(__VA_ARGS__)
#define FEI_7(X, ...) INCLUDE(X) NEW_LINE FEI_6(__VA_ARGS__)
#define FEI_8(X, ...) INCLUDE(X) NEW_LINE FEI_7(__VA_ARGS__)

#define INCLUDE_BLOCK_(_1,_2,_3,_4,_5,_6,_7,_8,NAME,...) NAME
#define INCLUDE_BLOCK(...) INCLUDE_BLOCK_(__VA_ARGS__, \
    FEI_8,FEI_7,FEI_6,FEI_5,FEI_4,FEI_3,FEI_2,FEI_1)(__VA_ARGS__)

If you stick this in a header file header_header, then you will be able to use it as follows:

#include <header_header>

INCLUDE_BLOCK(
    iostream,
    boost/asio.hpp,
    boost/bind.hpp,
    boost/date_time/posix_time/posix_time.hpp)

/* Write Some Code Here */

This solution is not all that practical, in order to compile your code you now need to run the preprocessing stage twice and insert the NEW_LINE characters.

gcc -E main.cpp -o main.e.cpp
sed -i 's/NEW_LINE/\n/g' main.e.cpp
g++ main.e.cpp -o a.out

It would be possible to extend this code to create a specific boost include block that removes the need to keep adding the boost part. One limit on this current implementation is that you can only include 8 headers.

Upvotes: 1

SigTerm
SigTerm

Reputation: 26409

You can't do that, because #include uses preprocessor, and preprocessor is dumb as rock.

You could, however, write your own additional preprocessor that takes *.cpp file as input and converts your extended #include syntax into standard syntax. Example of preprocessor is moc

Or you could put all includes into single file, but that'll add unnecessary dependencies and in the long run will increase compilation times.

Personally, I wouldn't bother.

Copy/paste means duplicating

Duplicating code (function bodies, for example) is bad. However, #include directive is not technically a code.

Upvotes: 5

Jarod42
Jarod42

Reputation: 217145

Some IDE/text editor have custom code snippets. Check if you have a plug-in for your tool.

Upvotes: 0

BitParser
BitParser

Reputation: 3968

One solution would be to put all those in a file "files_to_be_included.h"

files_to_be_included.h

#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

and then using

#include "files_to_be_included.h"

to include them all at once

Upvotes: 1

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272467

Is there any way to do it like this?

No.

The best you could do is put all your #include directives into a dedicated header file, and then #include that single header everywhere it's needed.

Upvotes: 8

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