I am running Ubuntu 12.04 and I'm currently working on a project involving C, OpenGL, a teapot and input methods.
The problem started when I decided to have arrow keys as input. I checked to see the key codes for arrow keys but all of the arrows return 0. I looked up how to get this to work and I found conio.h. Unfortunately, it is an old DOS header that is not available for Linux. Then I found a substitute called ncurses.
After installing the necessary libraries, by following the build instructions closely, I #included curses.h in my main.c source. When I first tried to compile using gcc, I got the following errors:
main.o:main.c:function _Key: error: undefined reference to 'stdscr'
main.o:main.c:function _Key: error: undefined reference to 'wgetch'
main.o:main.c:function _Key: error: undefined reference to 'stdscr'
main.o:main.c:function _Key: error: undefined reference to 'wgetch'
I found a fix by adding -lncurses to the makefile like so:
SOURCES=main.c
main: main.o
gcc -lm -lGL -lGLU -lglut -lncurses main.o -o main
main.o: main.c
gcc -lm -lGL -lGLU -lglut -c main.c
But I was greeted by another error:
/usr/bin/ld: error: cannot find -lncurses
As well as the previous errors.
I have spent the last 2 days searching both the Ubuntu forums and StackOverFlow. Any help would be appreciated.
P.S. I don't know if this is important but when I try to run /usr/bin/ld I get this error:
ld: fatal error: no input files
To resolve this problem, you should either provide the library file ( lib{nameOfTheLibrary}. so ) in those search paths or use -L command option. -L{path} tells the g++ (actually ld ) to find library files in path {path} in addition to default paths.
A message such as /usr/bin/ld: cannot find -linput actually means it was looking for a file named libinput.so . The -l flag is a command-line argument (to ld or to gcc ) that expects the library name to follow and then the library name is used to form the file name which includes the lib prefix and the .
LDFLAGS: Extra flags to give to compilers when they are supposed to invoke the linker, 'ld', such as -L. Libraries (-lfoo) should be added to the LDLIBS variable instead. LDLIBS: Library flags or names given to compilers when they are supposed to invoke the linker, 'ld'.
For anyone with the same problem I had: I was missing the 32 bit libraries; I was compiling 32 bit on a 64 bit server which was missing the lib32ncurses5-dev package.
On Ubuntu I simply ran:
sudo apt-get install lib32ncurses5-dev
First off, you should put the libraries after the object file when linking. And not have them at all in the compilation of of the source file.
After that, if ncurses is not installed in a standard search folder you need to point out to the linker where it is, this is done with the -L
command line option:
gcc main.o -o main -L/location/of/ncurses -lm -lGL -lGLU -lglut -lncurses
Try installing the ncurses-static
package too, if you have only the ncurses-devel
package installed in your Ubuntu OS.
If that solves your problem, plus if you add @Joachim's compiling instructions, you are off to a great start.
gcc main.o -o main -L/location/of/ncurses -lm -lGL -lGLU -lglut -lncurses
The linker can't find your shared library in it's search path. If you add the directory where your shared lib is to the LD_LIBRARY_PATH
environment variable the linker should find it and be able to link against it. In that case you could omit the -L
option to gcc:
gcc main.o -o main -lm -lGL -lGLU -lglut -lncurses
And it should compile fine.
EDIT:
Good to know that apt-get install libncurses5-dev
fixes your problem.
FYI.
The LD_LIBRARY_PATH
environment variable contains a colon separated list of paths that the linker uses to resolve library dependencies at run time. These paths will be given priority over the standard library paths /lib
and /usr/lib
. The standard paths will still be searched, but only after the list of paths in LD_LIBRARY_PATH
has been exhausted.
The best way to use LD_LIBRARY_PATH
is to set it on the command line or script immediately before executing the program. This way you can keep the new LD_LIBRARY_PATH
isolated from the rest of your system i.e. local to the current running running instance of shell.
$ export LD_LIBRARY_PATH="/path/to/libncurses/library/directory/:$LD_LIBRARY_PATH"
$ gcc main.o -o main -lm -lGL -lGLU -lglut -lncurses
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