Include headers in header file?

Question

I have several libraries made by myself (a geometry library, a linked list library, etc). I want to make a header file to include them all in one lib.h. Could I do something like this:

#ifndef LIB_H_
#define LIB_H_

#include <stdio.h>
#include <stdlib.h>
#include <linkedlist.h>
#include <geometry.h>
....

#endif

Then I could just reference this one library and actually reference multiple libraries. Is this possible? If not, is there a way around it?

James McNellis · Accepted Answer · 2010-04-20 23:25:43Z

21

Yes, this will work.

Note, however, that if you include a lot of headers in this file and don't need all of them in each of your source files, it will likely increase your compilation time.

It also makes it more difficult to figure out on which header files a particular source file actually depends, which may make code comprehension and debugging more difficult.

answered Apr 20, 2010 at 23:25

James McNellis

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3 Comments

epatel Over a year ago

It could also be a good thing if this lib.h where to be used as a precompiled header if the compiler support it (gcc does)

Mohit Deshpande Over a year ago

I was just using this as an example, I will probably only use this method for my libraries and not C libraries.

Clearer Over a year ago

I'm currently trying to port a game, as well as a support library, from windows to linux -- because of the "a single header to rule them all"-method it's a nightmare. Compilation time is massive and figuring out where anything belongs is virtually impossible. ANY change in any header file (and I need to do a lot of those) will force all source files to recompile. On top of that it's impossible to compile some header files (to check for errors) because they don't include anything themselves.

Matthew Flaschen · Accepted Answer · 2010-04-20 23:30:15Z

5

Yes, this works, and is in fact used in most APIs. Remember what a #include actually does (tell the preprocessor to immediately include a new file), and this should make sense. There is nothing to prevent several levels of inclusion, although implementations will have a (large) maximum depth.

As noted, you should organize your headers into logical groupings.

edited Apr 20, 2010 at 23:30

answered Apr 20, 2010 at 23:24

Matthew Flaschen

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1 Comment

elijahfhopp Over a year ago

Is there a name for these headers that only include other headers? I like your answer, +1

ManuelSchneid3r · Accepted Answer · 2016-11-16 12:42:48Z

4

The "right way" to include _{(in A)}

do nothing if: A makes no references at all to B
do nothing if: The only reference to B is in a friend declaration
forward declare B if: A contains a B pointer or reference: B* myb;
forward declare B if: one or more functions has a B object/pointer/reference as a parameter, or as a return type: B MyFunction(B myb);
#include "b.h" if: B is a parent class of A
#include "b.h" if: A contains a B object: B myb;

_{From a cplusplus.com article you should definitively read}

edited Nov 16, 2016 at 12:42

answered Oct 27, 2016 at 9:00

ManuelSchneid3r

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3 Comments

TobiMcNamobi Over a year ago

What about templates TemplateClass<B> mytemplateb;?

ManuelSchneid3r Over a year ago

I am not a guru, but both are classes (TemplateClass and B). Important is how you use them. Check the list above. Even its a template I dont think you need the definition if you dont need to know it. So probably you need inclusion only in case of value type aggregation or inheritance. Else a forward declaration should suffice. Yes templates can be forward declared too.

martinkunev Over a year ago

The question is not about C++

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