I'm not sure if the correct term is "build options". Here's the code that doesn't work :
#include <SDL2/SDL.h>
#include <SDL2/SDL2_gfxPrimitives.h>
polygonRGBA(renderer, x, y, 6, 255, 0, 0, 155); // this part
I've used this to compile it :
gcc -o test main.c `sdl2-config --cflags --libs̀
polygonRGBA() is a function from SDLGFX. It seems I've not added the correct options to build it (except this part, SDL2's compilation works). The given error is :
undefined reference to 'polygonRGBA'
What is the correct option to add ?
Generally, you can use pkg-config --list-all and grep for the name of the package you want to add compile or link flags for. But I was a little surprised to see that there is no pkg-config option for SDLGFX even though I have the -dev package installed on my (Ubuntu) system. Nor does sdl-config include the libraries for it (not that it necessarily should).
So try adding -lSDL2_gfx to your invocation,
gcc -o test main.c `sdl2-config --cflags --libs` -lSDL2_gfx
When pkg-config fails, you can make a good guess by searching for the library by name,
$ find /usr/lib | grep gfx
....
/usr/lib/x86_64-linux-gnu/libSDL2_gfx.so
...
and using -l with the part between lib and .so: libSDL2_gfx.so
Related
I'm trying to compile a client using hiredis in C on Mac OS X.
I've installed hiredis with:
brew install hiredis
But still get the error:
fatal error: 'hiredis.h' file not found
My hiredis.h is however in:
/usr/local/include/hiredis/hiredis.c
How do I tell the compiler this?
I'm compiling with:
gcc test.c -o test
In your question you said hiredis.h is in /usr/local/include/hiredis/hiredis.c, which doesn't really make any sense.
Assuming you meant that your hiredis.h is in /usr/local/include/hiredis. You can do like:
gcc test.c -I/usr/local/include/hiredis -o test
Read about -I in this SO post.
UPDATE:
As mentioned by #EricPostpischil in comments, its a better idea to just include like:
#include < hiredis/hiredis.h>
I am still not sure if /usr/local/include is in default include path. If it is, well no need to do anything, just compile like:
gcc test.c -o test
and if it isn't,
gcc test.c -I/usr/local/include -o test
If you have installed hiredis with homebrew, you can see what's in the package like this:
brew ls --verbose hiredis
/usr/local/Cellar/hiredis/0.14.0/INSTALL_RECEIPT.json
/usr/local/Cellar/hiredis/0.14.0/CHANGELOG.md
/usr/local/Cellar/hiredis/0.14.0/.brew/hiredis.rb
...
...
/usr/local/Cellar/hiredis/0.14.0/lib/libhiredis.dylib
/usr/local/Cellar/hiredis/0.14.0/lib/pkgconfig/hiredis.pc <--- PKG-CONFIG
/usr/local/Cellar/hiredis/0.14.0/lib/libhiredis.a
/usr/local/Cellar/hiredis/0.14.0/lib/libhiredis.0.14.dylib
...
...
And, as you can see, it gives you a pkg-config file with all the settings in it that you need. So, you might as well install pkg-config and do it properly!
brew install pkg-config
Now, if you want to know the C compiler flags for hiredis, you do:
pkg-config --cflags hiredis
-D_FILE_OFFSET_BITS=64 -I/usr/local/Cellar/hiredis/0.14.0/include/hiredis
And if you want to know the linker settings, you do:
pkg-config --libs hiredis
-L/usr/local/Cellar/hiredis/0.14.0/lib -lhiredis
And so, your compile-link command becomes very simple and updates itself when you update the packages:
gcc-9 $(pkg-config --cflags --libs hiredis) -o program program.c
I am trying to link GLFW to my C program.
The docs seem to suggest #include<GLFW/glfw3.h> however I have installed 2.7.2 (from my distro's repository) and don't have that header file:
find / -name *glfw* 2> /dev/null
/usr/lib/libglfw.so.2.6
/usr/lib/libglfw.a
/usr/lib/libglfw.so
/usr/lib/pkgconfig/libglfw.pc
/usr/lib/libglfw.so.2
/usr/include/GL/glfw.h
/usr/share/doc/libglfw-dev
/usr/share/doc/libglfw2
/var/cache/apt/archives/libglfw2_2.7.2-1_i386.deb
/var/cache/apt/archives/libglfw-dev_2.7.2-1_i386.deb
/var/lib/dpkg/info/libglfw2.list
/var/lib/dpkg/info/libglfw2.postinst
/var/lib/dpkg/info/libglfw-dev.md5sums
/var/lib/dpkg/info/libglfw2.postrm
/var/lib/dpkg/info/libglfw2.md5sums
/var/lib/dpkg/info/libglfw2.shlibs
/var/lib/dpkg/info/libglfw-dev.list
I tried #include<GL/glfw.h> but I still get undefined reference to 'glfwLoadTexture2D'
How do I link to GLFW and use glfwLoadTexture2D()?
An #include does nothing for the linker; it just brings in declarations, not the actual functions.
The documentation indicates that GLFW uses pkg-config (not surprising; #elmindreda knows her stuff), so your compilation line should be something like:
$ cc `pkg-config --cflags glfw3` -o foo foo.c `pkg-config --static --libs glfw3`
Also note that since the library uses pkg-config, you're not supposed to "care" about details such as where the header and library files are located on your particular installation. Just ask using the --cflags and --libs modes, and you will get the proper locations returned, as the example above indicates.
You are mixing up compilation and linking. If you were missing headers, you would probably have errors a lot sooner than the linking stage.
"Undefined reference" results from symbols not being found by the linker. The most likely cause is you not telling gcc that it should link to the GLFW libraries:
gcc myfile.c -lglfw
When I am on Linux, I compile opengl/glfw projects like this:
gcc main.c -lGL -lglfw
When I am on windows, I compile them by writing:
gcc main.c libglfw3.a -lopengl32 -lgdi32
and I put libglfw3.a file in the same directory where main.c is. I have read people say that they couldn't link properly before writing
-lopengl32 -lgdi32 -luser32 -lkernel32 -lws2_32.
Another thing which may be worth mentioning is that I couldn't link glfw libraries when I downloaded 32bit glfw binaries. When I downloaded 64bit glfw binaries everything worked fine. I have a 64 bit machine and a x86_64-w64-mingw32. I have read comments from people with the opposite experience, where they weren't able to link glfw libraries when they downloaded 64bit binaries, but they were able to link them after downloading 32bit binaries. My advice would be to try both.
I'm trying to compile some c code via make with gcc, but I keep getting:
/usr/bin/ld: cannot find -lnetlink
I have -lnetlink included in the gcc make parameters. Using locate netlink is able to find multiple items. I've even told gcc exactly where to find one by using -L/usr/include/linux, but it still gives the error.
The gcc command arguments below:
gcc -g -ggdb -Wall -Wextra -o mt6d mt6d.o address_worker.o tunnel_worker.o mt6d_assoc.o addr_gen.o send_utils.o if_utils.o tun_utils.o icmp_utils.o utils.o -lcrypto -lssl -lnetlink -lpthread -lnetfilter_queue
I've also been having errors with libnetlink.h, but was able to get them resolved, but I've included that here if that might be related and this error appears immediately after the other was fixed. Fixed by using C_INCLUDE_PATH
I've recently upgraded to Ubuntu 13.04 and was using 11.04 before that.
Let me know if you need any more information. Any help would be greatly appreciated!
Thanks,
-Alan
I'm trying to compile some c code via make with gcc, but I keep getting:
Technically, this stage is called linking. That difference may seem subtle at first, but it's a really important one and can help frame the investigation when problems like this arise.
You should not reference /usr/include paths with -L. -L adds to the search path for libraries and generally only header files should show up under /usr/include.
libnl enables pkg-config, so you should use that.
For example (assuming you have libnl-3-dev installed):
gcc -o my_executable $(pkg-config --libs libnl-3.0) my_foo.o my_bar.o
In a Makefile, you could do the following to achieve that effect:
LDLIBS+=$(shell pkg-config --libs libnl-3.0)
CFLAGS+=$(shell pkg-config --cflags libnl-3.0)
I'm trying to use in one of my projects. I'm working on a Mac, have gotten MacPorts with pkg-config and glib-2.0 packages.
When I try to make a file containing an include to above path, I get the following error (line above it is for clarity that it does actually give me the right dirs):
$ pkg-config --cflags --libs glib-2.0
-I/opt/local/lib/glib-2.0/include -I/opt/local/include -L/opt/local/lib -lglib-2.0 -lintl
$ make
gcc hash-glib.c -c `pkg-config --cflags --libs glib-2.0` -std=c99 -Wall -Wextra -pedantic -O2
hash-glib.c:2:23: error: glib/glib.h: No such file or directory
$
Presumably, you've run:
ls -l /opt/local/lib/glib-2.0/include/glib/glib.h \
/opt/local/include/glib/glib.h
to demonstrate that the header #include "glib/glib.h" actually is present in one of the locations where you've been told by pkg-config that it could be found. If it isn't there, then pkg-config is misleading you, and the compiler is telling you that you've been hoodwinked.
Since the compiler will have done its utmost to find the header, it is a reasonable bet that the file isn't in either of those locations. You are then left with detective work: where is the glib.h header installed?
find /opt/local -type f -name glib.h
If that tells you where it is, you can then work out what pkg-config should be saying. If that fails to find it, widen the search area. If you still can't find it, maybe it isn't installed yet? Or you only installed the glib runtime, not the development package.
I got a problem while installing the GNU Scientific Library (gsl).
I put the package on my desktop, and did "./configure", "make", and "sudo make install", according to the document included. I checked the /usr/local/include directory, there is a newly created "gsl" folder in there. But When I tried to use the functions provided by the library, the "undefined reference to 'gsl_sf_beta_inc'" error occurred. Here is my code.
#include <stdio.h>
#include <gsl/gsl_sf_gamma.h>
int main (void)
{
double a = 20;
double b = 1000;
double x = 0.5;
double result = gsl_sf_beta_inc(a, b, x);
printf("%f/d", result);
return 0;
}
I sensed that the problem might be caused by the fact I put the package on the desktop, so the binary code generated by the "make" command goes there, which is wrong.
So, is my guess correct? If it is, where should I put them? If it is not, what should I do?
Thanks.
You need to link the library, assuming the make install was successful.
The gsl's documentation says this should work
(note the two necessary linking options for gsl to work: "-lgsl -lgslcblas"):
gcc -I/usr/local/include -L/usr/local/lib main.c -o main -lgsl -lgslcblas -lm
Alternative "cblas" instead of gsl's cblas is also possible as per: alternate cblas for gsl
Use pkg-config --libs gsl to find out what the necessary linkers are to be and then just link them. An optional thing would be to check pkg-config --cflags gsl. The second gives you the directory of the include files if they are not installed in the default /usr/include/ directory. If you've installed it there you can just ignore that.
The output of pkg-config --libs gsl would be
-lgsl -lgslcblas -lm
That means that those three have to be linked. So while compiling your program you do that by,
gcc name.c -lgsl -lgslcblas -lm