which environmental variable indicates the list of all the directories which are searched in order to find out the header file included in a C file in the Linux kernel? I have some header files in a directory, and would like to include the path to that directory in the list of all directories searched. How may I do that? I tried exporting C_INCLUDE_PATH, but that doesn't remove the error, which says that it still can't find the header file.
Thanks,
D.
There is generally no environment variable that lists all of the directories searched for header files. The directories searched are a function of the compiler used. Your compiler almost certainly has a command-line switch to add a directory to the search list. E.g., for GCC and clang, consider the “-I” switch and related switches. Your compiler may also have environment variables where you can list directories to be added to the search list, such as C_INCLUDE_PATH. Keep in mind these likely list additional directories to search; they do not list all the directories searched.
Add -I/where/ever arguments to EXTRA_CFLAGS in your Makefile. Though generally this kind of thing is bad form. The kernel build includes its own include tree (and the local directory, of course). Is there a reason your code can't conform to the existing framework?
Related
I have found an unusual C makefile setup that relies upon a deprecated feature of GCC that appears to have no modern replacement.
This system needs to preprocess or 'cook' the local header files before including them. The makefiles take care of this and put the cooked versions in local './prepared/' directories. The header files are included as normal in the c using their normal names eg #include "name.h". The system simply needs './prepared/' to occur in the GCC header file search path before '.'.
Gcc used to offer the -I- option to remove the default '.' and allow the addition of header search path entries before it, but this option is deprecated.
From the gcc docs:
GCC looks for headers requested with #include "file" first in
the directory containing the current file, then in the directories
as specified by -iquote options, then in the same places it would
have looked for a header requested with angle brackets. For example,
if /usr/include/sys/stat.h contains #include "types.h", GCC looks
for types.h first in /usr/include/sys, then in its usual search path.
Is there no way to control the C header search path properly in gcc any more? Or is there another sensible way forward? I don't want to use a deprecated feature that may disappear. Right now I am sadly filtering the gcc deprecated feature warning messages to hide them. I didn't create the build environment, and it would be unpopular to solve the problem in a way that breaks the 'cookery'.
As far as I can tell, GCC provides no other means than the one you've described to avoid having each source file's directory first in the include search path used when compiling that file.
The best solution is probably to fix the headers and build system to get rid of header cooking. Such a scheme is very unusual -- pretty much everybody else gets by without.
If you must continue to rely on header cooking, then you probably should move the original headers to a directory that is not in the include search path. For example, create an "include" subdirectory of the main source directory, and put them there.
Edited to add:
Another alternative is to switch from the quoted include style to the angle-bracketed include style, and rely on -I options to set up the needed internal include directories however you want.
I'm trying to figure out how to add header and object files to the standard library so that I can use my custom files as easy as the standard library.
Currently I have to type the path to the header file in the .c file and then link the object file path when compiling.
I would like to just be able to add:
#include <mystdlib.h>
and not worry about linking the object file like I do when I reference the stdio.h header file.
I have searched around, but I fear I'm not using the proper terminology as I don't seem to find the results I need. Am I the first to want to do this, or it is just impossible, and therefore people don't even try?
gcc uses environment variables C_INCLUDE_PATH and LIBRARY_PATH to look for header and library files. Setting them somewhere (eg., your bash_profile) should achieve what you describe:
export C_INCLUDE_PATH="$HOME/include"
export LIBRARY_PATH="$HOME/lib"
Alternatively, the -I and -L flags add directories to the list of directories to be searched for header files and library files, respectively.
edit: As noted by #ChrisStratton below, the library name or object file needs to be explicitly specified. AFAIK, there is no way to make gcc always link against a library (like with libc).
sources:
https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html
https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html
ECB, cscope, xcscope. All working. Is cedet necessary?
MSVS, eclipse, code::blocks, xcode. All of them allow easy click on an included source file and take you to it.
Now, with the above setup, emacs does too.
Except emacs doesn't take you to the std:: libraries, doesn't assume their location in /src/linux or some such. Emacs is a little blind and needs you to manually set it up.
But I can't find anything that explains how to set up ff-find-other-file to search for any other directories, let alone standard major libraries, outside of a project's directory.
So, how do I do it?
Edit; Most important is to be able to request on either a file name (.h, .c, .cpp, .anything) or a library (iostream) and open the file in which the code resides.
Additional directories for ff-find-other-file to look into are in ff-search-directories variable which by default uses the value of cc-search-directories, so you should be able to customize any of the two to specify additional search paths.
As for the second question about requesting a file name and finding corresponding file, something like that will do:
(defun ff-query-find-file (file-name)
(interactive "sFilename: ")
;; dirs expansion is borrowed from `ff-find-the-other-file` function
(setq dirs
(if (symbolp ff-search-directories)
(ff-list-replace-env-vars (symbol-value ff-search-directories))
(ff-list-replace-env-vars ff-search-directories)))
(ff-get-file dirs file-name))
Call it with M-x ff-query-find-file or bind it to a key to your liking.
I developed small c application in linux. For this application i placed .h file in
linux standard path (/usr/include). Again i am compiling the same program
Output:
FATA ERROR : xyz.h(my own header file) not found
Do i need to update any variable in gcc or way to solve this problem
Thank You
Place the header file in the same directory as your .c file and use -I. when compiling
gcc -I. main.c -o myprog
You shouldn't place your header files in /usr/include that is meant for the system headers.
Note: you don't actually need the -I. because the current directory is searched by default, nevertheless, it doesn't hurt to add it.
Files specified by include directives are meant to be located in one of the search paths of the complier which are specified with the -I option in many cases (at least for gcc, is it the same for other compilers?). The search paths are verified in the order of definition in the command line.
There are 2 kinds of include directives:
double quoted ones (#include "xyz.h")
angle bracket ones (#include <xyz.h>)
IIRC, the default and first search path for the former is the working directory. For the later, it's compiler dependant, but it's usually /usr/include/.
Depending of the include directive you used, you should pick the right location for your file. Or better, put your file in a good location (say the same place as the including file), and add a search path to your gcc command.
You should separate your header .h files, from system and repository built headers so you don't break anything.
I would recommend making a folder in your home directory called include and just adding it to your path, that way you never have to worry about it again and no need for the -I/flag
I wanted to include a file say a.h in my program which is located at some location say (/ws/uname/bd/lib) & that file in turn has different include statements whose files are located in vastly different locations.
How can i do that by just including the file with "/ws/uname/bd/lib/a.h".
I dont want to change any of the header file.
Appreciate your help
What compiler are you using? If it's clang or gcc, you can use the -I flag to add search paths for header files. From the gcc(1) man page:
-Idir
Add the directory dir to the head of the list of directories to be searched for header files. This can be used to override a system header file, substituting your own version, since these directories are searched before the system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files (use -isystem for that). If you use more than one -I option, the directories are scanned in left-to-right order; the standard system directories come after.