I've been trying all day to build and run a simple Ruby inside of C program.
This is a recurring topic here, and none of them are identical to my issue nor have any of the solutions helped me. I have the ruby-dev installed.
The pkg-config command gives this:
$ pkg-config --cflags --libs ruby-2.7
-I/usr/include/x86_64-linux-gnu/ruby-2.7.0 -I/usr/include/ruby-2.7.0 -lruby-2.7 -lm
The compile command gives this:
$ gcc -I/usr/include/x86_64-linux-gnu/ruby-2.7.0 -I/usr/include/ruby-2.7.0 -I. -lruby-2.7 -o hello *.c
/usr/bin/ld: /tmp/ccdKXtnU.o: in function 'main':
hello.c:(.text+0x9): undefined reference to 'ruby_setup'
collect2: error: ld returned 1 exit status
I have tried switching up the order of the includes. I have tried removing one then the other include. I have tried using a Makefile and running it thru make. I have tried breaking the program up into multiple files. I have tried symbolically linking the architecture relative config.h file into the main header file directory.
The only thing I can think of that I haven't tried is putting the name of the ruby object library that needs to be linked in on the command line, but I don't know the name, or location, of that file.
Here's the latest rendition of the program:
#include <stdio.h>
#include <ruby.h>
int main(void)
{
if (ruby_setup()){
puts("Hola!");
}
else{
printf("Hello World\n");
}
return(0);
}
One of the reasons that pkg-config separates cflags and libs is that they go in different places in the command-line (and sometimes different commands).
If you're going to compile and link in one command, it goes like this:
c99 -o hello $(pkg-config --cflags ruby-2.7) *.c $(pkg-config --libs ruby-2.7)
There's a certain logic to this arrangement. First, we tell the compiler where to look for header files (which it must see before it compiles your program), then where to find the program to compile, and finally where to find the libraries which are referred to by the program.
Related
probably this is a trivial newbie question, however, I can't figure out how to solve it.
I'm trying to build a test program using libtiff (test program copied from here). I've downloaded the static library libtiff.lib as well as the required header file tiffio.h. When I compile the main c function with no problem I have a main.o file. When I try to link main.o with libtiff using this command
gcc -g -Wall -o test.exe ./libtiff.lib ./test.o
I have this error:
undefined reference to `_imp__TIFFOpen'
I've looked into the lib file with nm -A libtiff.lib command and I can find this line
libtiff.lib:libtiff3.dll:00000000 I __imp__TIFFOpen
but it has 2 leading underscores instead of 1 as required by the linker. I'm using mingw on Windows 7 and all the required files are in the same directory.
No clue how to link with no errors.
Thanks in advance.
As suggested in the the comments, it was sufficient to invert the order of objects passed as arguments:
gcc -g -Wall -o test.exe ./test.o ./libtiff.lib
I want to compile a small program which has a pretty straight forward makefile, but I seem unable to get it working. Maybe you can help me. The makefile has the following targets:
visca-cli: visca-cli.c libvisca_hl.o
gcc -Wall -o visca-cli visca-cli.c /usr/local/lib/libvisca.so libvisca_hl.o
libvisca_hl.o: libvisca_hl.c
gcc -Wall -c libvisca_hl.c
I can 'make libvisca_hl.o' successfully and create the .o file. But 'make visca-cli' fails with error messages like
libvisca_hl.c:(.text+0x468a): undefined reference to
`VISCA_get_md_disptime'
for every single function defined in libvisca.h (here it's VISCA_get_md_disptime)
Here are the include sections from the various files (ommitting standard libraries):
In visca-cli.c:
#include "libvisca.h"
#include "libvisca_hl.h"
In libvisca_hl.c:
#include "libvisca_hl.h"
In libvisca_hl.h:
#include "libvisca.h"
All includes quoted with "" are present in the local directory where I run make and where all the sourcefiles are. There are no subfolders. So I guess the problem lies with the makefile? Any help appreciated!
The order of libraries and objects on your compilation/link command line matters. In your case, you just need to put the shared object at the end:
gcc -Wall -o visca-cli visca-cli.c libvisca_hl.o /usr/local/lib/libvisca.so
On most systems /usr/local/lib is already part of the standard library search path, so you could simplify further:
gcc -Wall -o visca-cli visca-cli.c libvisca_hl.o -lvisca
I need to use erl_interface in my C-program. There is Erlang R15B01 on Debian Wheezy.
I just do the following (for example).
// main.c
#include <ei.h>
#include <erl_interface.h>
int main() {
erl_init(NULL,0);
return 0;
}
Then i say:
cc -I/usr/lib/erlang/lib/erl_interface-3.7.7/include -L/usr/lib/erlang/lib/erl_interface-3.7.7/ -lei -lerl_interface -o prog main.c
Directory specified as -L contains libei.a and liberl_interface.a but linker abusing that reference to erl_init is undefined: undefined reference to erl_init
What may be wrong? Sorry for really stupid question.
Newest versions of the GNU toolchain require that the object files and libraries be specified in the same order their symbols depend on each other. So you should generally put the library flags to the end of the invocation, like this:
gcc -o prog main.c -L<libdir> -I<includedir> -lerl_interface -lei
I am having trouble installing a dependency for a program that itself depends on pcre.h. I have this installed to /opt/local/include, but the C compiler does not see it and thus gives me:
error: pcre.h: No such file or directory
I have confirmed this by writing a hello world program that tries to include it:
#include <pcre.h>
#include <stdio.h>
int main(void)
{
printf("hello, world\n");
return 0;
}
This also gives the error unless I specify the path as </opt/local/include/pcre.h>.
I would like the C compiler to find this by default but I do not know where this is configured. Tab completion hasn't revealed any HEADER_PATH environment variables and I cannot find anything like it that isn't specific to XCode. I am, however, using Mac OSX Snow Leopard on the off chance that makes a difference.
Use -I /opt/local/include on the command line or C_INCLUDE_PATH=/opt/local/include in the environment.
Use the pcre-config utility to get the right flags:
$ pcre-config --libs --cflags
-L/opt/local/lib -lpcre
-I/opt/local/include
If you're compiling via the command line,
$ gcc -Wall -g `pcre-config --libs --cflags` main.c
I'm trying to start developing a program using ncurses on Linux. I can't even get the Hello World example to compile. Here's the code:
#include <curses.h>
int main()
{
initscr();
printw("Hello, world.");
refresh();
getch();
endwin();
return 0;
}
When I attempt to compile, I get:
hello.c:(.text+0x12): undefined reference to `initscr'
For every one of those called functions.
I installed ncurses via apt-get, and also by downloading the sources and compiling, installing, etc.
I have tried #include both curses.h and ncurses.h.
What is going on?
Have you used the -lcurses option when linking?
Including the header files let the code compile (because the compiler knows what the function call looks like from the .h file), but the linker needs the library file to find the actual code to link into your program.
As Greg Hewgill said, you need to pass in -lcurses or -lncurses to link to the curses library.
gcc -o hello hello.c -lncurses
You also probably mean to use initscr() and getch(). Once I make those substitutions, the above compiles for me.
I was having a similar issue and found a solution which helped me, but was slightly different from the other answers posted here. I was trying to use the panels library with curses and my compile command was:
$ gcc -o hello hello.c -lncurses -lpanel
when I read the other answers, I was baffled because I was including the -lncurses flag, but it still was not compiling, and with similar errors to what you were getting:
$ gcc -o hello hello.c -lncurses -lpanel
/usr/lib/gcc/i686-linux-gnu/4.7/../../../../lib/libpanel.a(p_new.o): In function `new_panel':
p_new.c:(.text+0x18): undefined reference to `_nc_panelhook'
I finally found my answer in the tldp:
"To use panels library functions, you have to include panel.h and to link the program with panels library the flag -lpanel should be added along with -lncurses in that order."
So, it appears that order is important when using the compile flags! I tried switching the order:
gcc -o hello hello.c -lpanel -lncurses
This allowed it to compile successfully. I know you already have your answer, so I hope this helps someone.
For anyone having similar problems: -lx arguments, where x is your library, should always follow the source and object files.