I cannot make rpath work properly and make my binary to search for the library in the specified folder:
I have 3 very simple files:
main.c
#include <stdio.h>
#include <func.h>
int main() {
testing();
return 1;
}
func.h
void testing();
func.c
#include "func.h"
void testing(){
printf(testing\n");
}
Then I proceed to create a shared library as it follows:
gcc -c -fpic func.c -o ../release/func.o
gcc -shared -o ../release/lib/lib_func.so ../release/func.o
And then compile the program:
gcc main.c ../release/lib/lib_time_mgmt.so -Wl,-rpath=/home/root/ -o ../release/main
I receive the next warning:
main.c:7:2: warning: implicit declaration of function ‘testing’ [-Wimplicit-function-declaration]
testing();
But besides it, the program works fine.
However, my problem is that if now I want to move the library to /home/root (as specified in rpath) it does not work and the library is still searched only in the path specified when I compiled the main.c file which is ../release/lib/lib_time_mgmt.so
What am I doing wrong?
EDIT: After accepting the answer, I leave here the exact line as I used it and made it work for whoever might find it useful:
gcc main.c -L/home/root -Wl,-rpath,'/home/root/' -l:libtime_mgmt -o ${OUT_FILE}
Note: the rpath was used with the path betwen simple '. Not sure if that was the reason why it was not working before, but it worked this way now.
rpath is not used at compile time, but rather at link/runtime... thus you probably need to use both of these:
-L /home/root - to link correctly at build time
-Wl,-rpath=/home/root - to link correctly at run-time
You should use the -l ${lib} flag to link with libraries, don't specify their path as an input.
In addition to this, convention states that the libraries are named libNAME.so - e.g:
-l func will try to link with libfunc.so
-l time_mgmt will try to link with libtime_mgmt.so
Once you've addressed the above points, try the following:
gcc main.c -L/home/root -Wl,-rpath=/home/root -lfunc -ltime_mgmt -o ${OUT_FILE}
As a final point, I'd advise that you try not to use rpath, and instead focus on installing libraries in the correct places.
Unrelated to your question, but worth noting. Your use of #include <...> vs #include "..." is questionable. See: What is the difference between #include <filename> and #include "filename"?
Related
I have this simple code:
max = (int) sqrt (number);
and in the header I have:
#include <math.h>
But application still says undefined reference to sqrt. Do you see any problem here? It looks like everything should be okay.
You may find that you have to link with the math libraries on whatever system you're using, something like:
gcc -o myprog myprog.c -L/path/to/libs -lm
^^^ - this bit here.
Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function.
Failing that, you'll need to show us your code, your compile command and the platform you're running on (operating system, compiler, etc).
The following code compiles and links fine:
#include <math.h>
int main (void) {
int max = sqrt (9);
return 0;
}
Just be aware that some compilation systems depend on the order in which libraries are given on the command line. By that, I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence.
So, for example, given the commands:
gcc -o plugh plugh.o -lxyzzy
gcc -o plugh -lxyzzy plugh.o
and plugh.o requires something from the xyzzy library, the second may not work as you expect. At the point where you list the library, there are no unresolved symbols to satisfy.
And when the unresolved symbols from plugh.o do appear, it's too late.
I suppose you have imported math.h with #include <math.h>
So the only other reason I can see is a missing linking information. You must link your code with the -lm option.
If you're simply trying to compile one file with gcc, just add -lm to your command line, otherwise, give some informations about your building process.
Just adding the #include <math.h> in c source file and -lm in Makefile at the end will work for me.
gcc -pthread -o p3 p3.c -lm
Here are my observation, firstly you need to include the header math.h as sqrt() function declared in math.h header file. For e.g
#include <math.h>
secondly, if you read manual page of sqrt you will notice this line Link with -lm.
#include <math.h> /* header file you need to include */
double sqrt(double x); /* prototype of sqrt() function */
Link with -lm. /* Library linking instruction */
But application still says undefined reference to sqrt. Do you see any
problem here?
Compiler error is correct as you haven't linked your program with library lm & linker is unable to find reference of sqrt(), you need to link it explicitly. For e.g
gcc -Wall -Wextra -Werror -pedantic test.c -lm
I had the same issue, but I simply solved it by adding -lm after the command that runs my code.
Example.
gcc code.c -lm
I have this simple code:
max = (int) sqrt (number);
and in the header I have:
#include <math.h>
But application still says undefined reference to sqrt. Do you see any problem here? It looks like everything should be okay.
You may find that you have to link with the math libraries on whatever system you're using, something like:
gcc -o myprog myprog.c -L/path/to/libs -lm
^^^ - this bit here.
Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function.
Failing that, you'll need to show us your code, your compile command and the platform you're running on (operating system, compiler, etc).
The following code compiles and links fine:
#include <math.h>
int main (void) {
int max = sqrt (9);
return 0;
}
Just be aware that some compilation systems depend on the order in which libraries are given on the command line. By that, I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence.
So, for example, given the commands:
gcc -o plugh plugh.o -lxyzzy
gcc -o plugh -lxyzzy plugh.o
and plugh.o requires something from the xyzzy library, the second may not work as you expect. At the point where you list the library, there are no unresolved symbols to satisfy.
And when the unresolved symbols from plugh.o do appear, it's too late.
I suppose you have imported math.h with #include <math.h>
So the only other reason I can see is a missing linking information. You must link your code with the -lm option.
If you're simply trying to compile one file with gcc, just add -lm to your command line, otherwise, give some informations about your building process.
Just adding the #include <math.h> in c source file and -lm in Makefile at the end will work for me.
gcc -pthread -o p3 p3.c -lm
Here are my observation, firstly you need to include the header math.h as sqrt() function declared in math.h header file. For e.g
#include <math.h>
secondly, if you read manual page of sqrt you will notice this line Link with -lm.
#include <math.h> /* header file you need to include */
double sqrt(double x); /* prototype of sqrt() function */
Link with -lm. /* Library linking instruction */
But application still says undefined reference to sqrt. Do you see any
problem here?
Compiler error is correct as you haven't linked your program with library lm & linker is unable to find reference of sqrt(), you need to link it explicitly. For e.g
gcc -Wall -Wextra -Werror -pedantic test.c -lm
I had the same issue, but I simply solved it by adding -lm after the command that runs my code.
Example.
gcc code.c -lm
I've been working on a module in C (under Linux) that requires another module (headers are in other directories).
My problem is that when I compile the code with my Makefile, the gcc compiler tells me that some headers aren't found.
gcc -c render.c
So I include the directories to find the header but here, gcc tries to find the "main" function which does not exist: it is a module...
gcc /opt/vc/include -c render.c
So I would like to know how is it possible to compile a module (output in module.o) that requires other modules?
Here are my files:
render.c:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include "render.h"
int width,height;
int loop,counter;
int initRender(void(*setup)(void),void(*draw)(void),void(*end)(void))
{
init(&width, &height);
loop = -1;
counter = 0;
setup();
while(loop==-1)
{
Start(width, height);
draw();
End();
counter++;
}
end();
finish();
exit(0);
return 0;
}
render.h:
#include "VG/openvg.h"
#include "VG/vgu.h"
#include "fontinfo.h"
#include "shapes.h"
#ifndef RENDER_H_
#define RENDER_H_
extern int width,height;
extern int loop,counter;
int initRender(void(*setup)(void),void(*draw)(void),void(*end)(void));
#endif
Makefile:
INCLUDEFLAGS=-I/opt/vc/include -I/opt/vc/include/interface/vmcs_host/linux -I/opt/vc/include/interface/vcos/pthreads -IopenVG
LIBFLAGS=-L/opt/vc/lib -lGLESv2 -lEGL -lbcm_host -lpthread -ljpeg -LopenVG
NEEDED= openVG/libshapes.o openVG/oglinit.o
all: render
render.o: render.c
gcc -Wall -g $(INCLUDEFLAGS) -c render.c
You probably want
gcc -Wall -g -I/opt/vc/include -c render.c
this will produce a render.o object file.
Please take time to read the documentation about invoking GCC. In particular, check what every option -Wall, -g, -I and -c means. IMHO the first two are very important.
Later, you probably want to link all your object files into an executable, with some external libraries. Perhaps you want something like
gcc -g -Wall -L/opt/vc/lib render.o main.o -lvc -o myprogram
(you really want the -Wall and -g options; IMHO you need to be an expert to dare avoiding them; once you have debugged your program and want to benchmark it, add -O2 for optimizations)
But surely, you want other options.
Notice that order of arguments to gcc matters a lot
Of course, you should learn about GNU make and you need to use it. See this and that examples. You might use make --trace (with recent make) or remake to debug your Makefile (which is not good). You should also run once make -p to understand more the builtin rules of make.
Perhaps you want a library, then read the Program Library HowTo.
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 have this simple code:
max = (int) sqrt (number);
and in the header I have:
#include <math.h>
But application still says undefined reference to sqrt. Do you see any problem here? It looks like everything should be okay.
You may find that you have to link with the math libraries on whatever system you're using, something like:
gcc -o myprog myprog.c -L/path/to/libs -lm
^^^ - this bit here.
Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function.
Failing that, you'll need to show us your code, your compile command and the platform you're running on (operating system, compiler, etc).
The following code compiles and links fine:
#include <math.h>
int main (void) {
int max = sqrt (9);
return 0;
}
Just be aware that some compilation systems depend on the order in which libraries are given on the command line. By that, I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence.
So, for example, given the commands:
gcc -o plugh plugh.o -lxyzzy
gcc -o plugh -lxyzzy plugh.o
and plugh.o requires something from the xyzzy library, the second may not work as you expect. At the point where you list the library, there are no unresolved symbols to satisfy.
And when the unresolved symbols from plugh.o do appear, it's too late.
I suppose you have imported math.h with #include <math.h>
So the only other reason I can see is a missing linking information. You must link your code with the -lm option.
If you're simply trying to compile one file with gcc, just add -lm to your command line, otherwise, give some informations about your building process.
Just adding the #include <math.h> in c source file and -lm in Makefile at the end will work for me.
gcc -pthread -o p3 p3.c -lm
Here are my observation, firstly you need to include the header math.h as sqrt() function declared in math.h header file. For e.g
#include <math.h>
secondly, if you read manual page of sqrt you will notice this line Link with -lm.
#include <math.h> /* header file you need to include */
double sqrt(double x); /* prototype of sqrt() function */
Link with -lm. /* Library linking instruction */
But application still says undefined reference to sqrt. Do you see any
problem here?
Compiler error is correct as you haven't linked your program with library lm & linker is unable to find reference of sqrt(), you need to link it explicitly. For e.g
gcc -Wall -Wextra -Werror -pedantic test.c -lm
I had the same issue, but I simply solved it by adding -lm after the command that runs my code.
Example.
gcc code.c -lm