Various resources have mentioned about the -I option of gcc , but have not mentioned its syntax. I want to add a header file which is not present in the default directory which are taken into consideration by the compiler for adding the header files at the compile time. How can I achieve it?
Just as the man page says, follow the argument directly with the path.
gcc ... -I/path/to/headers ...
You can use the -I option:
gcc -o foobar -I/path/to/headers -I/path/to/other foobar.c
You can also use the C_INCLUDE_PATH environment variable. You could set this up in your makefile:
C_INCLUDE_PATH = /path/to/headers:/path/to/other
foobar: foobar.c
gcc -o foobar foobar.c
You can either add a -I option to the command line to tell the compiler to look there for header files. If you have header files in include/ directory, then this command should work for you.
gcc -Iinclude/
There shouldn't be any space between -I compiler option and directory location.
If, you are using makefile, you can include this option in CFLAGS macro in your makefile.
CFLAGS = -Iinclude/ -c -Wall
OR
You can include header files using #include "../include/header.h".
Have a look at this answer.
Related
I found a useful library on github for my project, after building this later I tried to use some predefined function on it. I couldn't compile my project because there is some header file missing like this one :
In file included from main.c:2:0:
ptask.h:11:19: fatal error: ptime.h: No such file or directory
I compiled my project using this command :
gcc main.c -L. -lptask
This is all the files in project folder :
libptask.a main.c ptask.h
This is the library content:
$ ar -t libptask.a
pbarrier.c.o
pmutex.c.o
ptask.c.o
ptime.c.o
rtmode.c.o
tstat.c.o
libdl.c.o
dle_timer.c.o
calibrate.c.o
Do I need to add all the headers of this files or just link the lib when compiling ?
Your main.c #include-s ptask.h which in turn #include-s ptime.h. Having compiled static libs alone is not enough (that's the linker's job), you still need to have all used header files (which is the compiler's job), both the ones you use and their dependencies, recursively applicable.
Normally you need to be sure that the header files are in your "include path", something that a lot of compilers define with -I as a command-line option. You'll need to include the source directory of that library, or if it has a make install option, then the place where they got installed.
regarding:
gcc main.c -L. -lptask
this is performing the compile step and the link step in one command.
It is also not enabling the warnings, which should always be enabled during the compile step.
Suggest something similar to the following to compile
gcc -Wall -Wextra -Wconversion -pedantic -std=gnu11 -g -c main.c -o main.o -I.
and when you have fixed all the warnings, then use something similar to the following to link
gcc main.o -o main -L. -lptask
I'm trying to compile my C code but I need to tell the GCC compiler where two file are.
The two files are located here
/usr/local/ssl/include/
/usr/local/ssl/lib/
I want to add this to my gcc -o file file.c so that my program can work.
In gcc, the -I option is used for adding a directory to the set of directories to search for header files, and the -L option is used for adding a directory to the set of directories to search for libraries. Since you're not explicitly linking in any libraries, you shouldn't need the -L option in this case.
gcc -I/usr/local/ssl/include -o file file.c
If you were linking in libraries, something like the following format should work, assuming that file.c calls a function in libmyLib.a:
gcc -I/usr/local/ssl/include -o file file.c -L/path/to/my/library -lmyLib
See this question for more details regarding library linking order.
I have the following makefile
CXXFILES = pthreads.cpp
CXXFLAGS = -O3 -o prog -rdynamic -D_GNU_SOURCE -L./libmine
LIBS = -lpthread -ldl
all:
$(CXX) $(CXXFILES) $(LIBS) $(CXXFLAGS)
clean:
rm -f prog *.o
I am trying to include the ./libmine library within CXXFLAGS, but it seems like it is not the right way to include a static library, because when I compile the program, I get many undefined references error. So what is actually the right way to include a static library in the makefile?
use
LDFLAGS= -L<Directory where the library resides> -l<library name>
Like :
LDFLAGS = -L. -lmine
for ensuring static compilation you can also add
LDFLAGS = -static
Or you can just get rid of the whole library searching, and link with with it directly.
Say you have main.c, fun.c and a static library libmine.a.
Then you can just do in your final link line of the Makefile
$(CC) $(CFLAGS) main.o fun.o libmine.a
CXXFLAGS = -O3 -o prog -rdynamic -D_GNU_SOURCE -L./libmine
LIBS = libmine.a -lpthread
Make sure that the -L option appears ahead of the -l option; the order of options in linker command lines does matter, especially with static libraries. The -L option specifies a directory to be searched for libraries (static or shared). The -lname option specifies a library which is with libmine.a (static) or libmine.so (shared on most variants of Unix, but Mac OS X uses .dylib and HP-UX used to use .sl). Conventionally, a static library will be in a file libmine.a. This is convention, not mandatory, but if the name is not in the libmine.a format, you cannot use the -lmine notation to find it; you must list it explicitly on the compiler (linker) command line.
The -L./libmine option says "there is a sub-directory called libmine which can be searched to find libraries". I can see three possibilities:
You have such a sub-directory containing libmine.a, in which case you also need to add -lmine to the linker line (after the object files that reference the library).
You have a file libmine that is a static archive, in which case you simply list it as a file ./libmine with no -L in front.
You have a file libmine.a in the current directory that you want to pick up. You can either write ./libmine.a or -L . -lmine and both should find the library.
The -L merely gives the path where to find the .a or .so file. What you're looking for is to add -lmine to the LIBS variable.
Make that -static -lmine to force it to pick the static library (in case both static and dynamic library exist).
Addition: Suppose the path to the file has been conveyed to the linker (or compiler driver) via -L you can also specifically tell it to link libfoo.a by giving -l:libfoo.a. Note that in this case the name includes the conventional lib-prefix. You can also give a full path this way. Sometimes this is the better method to "guide" the linker to the right location.
I'm trying to compile a C program (myProgram.c) that includes a custom .h file that is in a specified directory. How can I add the directory to gcc so that I can build myProgram.c anytime using just a command like gcc myProgram (with no flags and what not)
You can do this by altering the C_INCLUDE_PATH environment variable, e.g.
C_INCLUDE_PATH=~/include
export C_INCLUDE_PATH
You can add that to your .bashrc or .bash_profile or whatever to always have the environment variable set properly. Here's a reference on how you can do the same for libraries and C++.
had to use a whole set of flags to get this working on El Capitan:
export DYLD_LIBRARY_PATH=/usr/local/include
export CPPFLAGS="-I/usr/local/include/snappy-c.h"
export CFLAGS="-I/usr/local/include/snappy-c.h"
export CXXFLAGS="-I/usr/local/include/snappy-c.h"
export LDFLAGS="-L/usr/local/lib"
Makefiles would be helpful in this situation, they ease the compilation of multiple file projects.
Assuming you are using these same files and they are in the same directory
main.c
custom.c
custom.h
A sample makefile could look like
all: main.o custom.o
gcc main.o custom.o -o myExecutable
main.o: main.c
gcc -c main.c
custom.o: custom.c custom.h
gcc -c custom.c
clean:
rm -f *.o myExecutable
Or something similar, the general format is
name: dependency
command
So by running make all from the commandline you would be instructing the compiler to compile your source code into object files, and then link those object files together into an executable.
Make should be easily available on any modern system. For more information on basic makefiles and usage refer to this simple tutorial: http://mrbook.org/tutorials/make/
This is the header file and its C file:
cs50.h and
cs50.c
Now I use them in the following example http://www.paste.ubuntu.com/576370/ — which is no longer available.
I already put the header file in /usr/bin/include or something like that and when I try to compile my code using gcc -o xxx xxx.c, it doesn't work, so tried to fix this and the following way worked: http://www.paste.ubuntu.com/576371/ — which is no longer available.
Now I want to do something to make the 'make' command work as the gcc does.
What do I need to do?
The following was the old topic:
I was using gcc command to
compile C programs but after a period
of time I got a problem. I need
to compile a new header file and use
it as a library.
The header file called cs50.h.
so after doing it and it's ok I can
compile using the following
gcc -o xxx xxx.c -lcs50
It works but now I want to use 'make'
command and I can't get it to work.
It just don't compile the header file
and library as gcc was before I edit
it to accept the cs50 library.
So now I want to add to the 'make'
command the following: -lcs50
Can anyone help me in this please?
Near the top of your Makefile, add the line:
LDLIBS = -lcs50
If you are using Make's default (implicit) rules for the building, then that is all you need to do. If you are using explicit rules, you will need to add $(LDLIBS) to your explicit rules.
If there is no Makefile, then make is using default rules, and you can either just create a makefile with
echo LDLIBS = -lcs50 > Makefile
or tell make to link with certain libraries by specifying the required libraries in LDLIBS in the environment. For example, if you are using a sh-derived shell (anything other than csh or tcsh) you can do:
LDLIBS=-lcs50 make target
If you are using a csh variant, you can do:
env LDLIBS=-lcs50 make target
or just do (again, for non-csh shells)
export LDLIBS=-lcs50
before running make. (For csh variants, do setenv LDLIBS -lcs50)
You can use below “make” command to link library and include header directories,
make <.c or .cpp source filename_without_extension> LDLIBS="-l<lib1> -l<lib2>"
suppose you have server.cpp file to compile using make command,
make server LDLIBS="-lcpprest -lpthread -lssl -lcrypto" LDFLAGS="-L/usr/lib/" CXXFLAGS="-I/usr/include/"
Output will expand the compilation command as,
g++ -I/usr/include/ -L/usr/lib/ server.cpp -lcpprest -lpthread -lssl -lcrypto -o server
Did you forget that you have to tell gcc in what directory the CS50 library is located?
gcc … -L/directory/for/cs50_library -lcs50