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User versus System include, quotes and brackets etc.

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In the process of writing a series of articles I realized that I stopped using the preprocessor differentiation of user and system paths in the "technically" correct manner.  Part of this is on purpose but part is basically because I don't find the differentiation particularly useful anymore.  Anyway, the question is how you use includes and how much you use the different path rules and why?

 

 

With Gcc/Clang you have -I and -iquote options to control the different paths between quoted and bracketed.  As far as I can remember, Cl (Visual Studio) supplies no '-iquote' style variation so the only difference is the search of the local or relative directories between brackets and quotes.

 

My thinking is that, obviously there is a notable difference and I do use it correctly in most cases I believe.  '#include "item"' looks in the current directory first, so unless the current code location has been added to the search path, this is how you get at local headers.  For almost every other usage though, I rely on controlling the include path order and using naming/nesting habits which avoid conflicts.  Someone ran into conflicts recently with 'math.h' which in conjunction with proofing the code made me think about this problem and how I had been writing code to avoid it.

 

Other than local, or relative to the current directory, searches, what other reasons do folks use the quoted versions for?  I realized my example code needed a fix since my reasons for using quotes and brackets didn't match what I put in the example code.  Oops.  But as stated, it got me to thinking about this and how others deal with it.  I might even turn it into a little article for fun. smile.png

Edited by All8Up

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Technically there doesn't have to be a stdio nor stdlib file. The compiler is allowed to supply them internally (or any which way the implementer desires).

 

So

#include "stdio"

is pedantically incorrect and unportable code as it requires the file "stdio" to exist.

#include <stdio>

is how the compiler is told find-the-system-header called 'stdio'.

 

In practice every C/C++ compiler I know of uses files for the standard headers so it ends up not mattering much.

 

Not every compiler will even honor the system folders vs current folder rule. Many require you to give them an explicit list of include directories and they always search them in order.

Edited by Shannon Barber

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Guest Hiwas

Technically there doesn't have to be a stdio nor stdlib file. The compiler is allowed to supply them internally (or any which way the implementer desires).

 

So

#include "stdio"

is pedantically incorrect and unportable code as it requires the file "stdio" to exist.

#include <stdio>

is how the compiler is told find-the-system-header called 'stdio'.

Yeah, I've seen a couple odd compilers for embedded systems which do some of these things.  Of course this was "way" back with C only.  I had hoped such things went out of style in the last 15 or so years.  Of course, you never know so yup, this is one I try to do correctly at all times..

 

In practice every C/C++ compiler I know of uses files for the standard headers so it ends up not mattering much.

 

Not every compiler will even honor the system folders vs current folder rule. Many require you to give them an explicit list of include directories and they always search them in order.

 

I'd be curious if you know any current semi-mainstream compilers with this behavior?  I've seen goofy ass behavior on and off but usually in really limited special purpose environments.  Are there are any in use, fairly mainstream compilers, doing this that you've seen?  I.e. places you might want to build a game would be my primary interest of course.

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My rule is usually to use brackets for STL, Standard Library, OS APIs (e.g. Win32), and External Dependencies (outside my project hierarchy) and quotes for Internal Dependencies (in a folder that holds all 3rd-party code and libraries in my project hierarchy) and project headers.

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