I am trying to learn OpenMP, starting with the following simple snippet
#include <stdio.h>
#include <stdlib.h>
int main(void) {
#pragma omp parallel
printf("Hello OpenMP!\n");
return 0;
}
Simply compiling from the command line works:
cls ~/Desktop $ gcc -fopenmp HelloOpenMP.c -o HelloOpenMP
cls ~/Desktop $ ./HelloOpenMP
Hello OpenMP!
Hello OpenMP!
However, I'd like to use Eclipse with CDT. I created a new build configuration "OpenMP" and tried to add the -fopenmp flag under "Miscellaneous", copying the other settings from the "Debug" build configuration.
The build fails with
14:56:16 **** Incremental Build of configuration OpenMP for project HelloOpenMP ****
make all
Building file: ../src/HelloOpenMP.c
Invoking: GCC C Compiler
gcc -O0 -g3 -Wall -c -fmessage-length=0 -fopenmp -MMD -MP -MF"src/HelloOpenMP.d" -MT"src/HelloOpenMP.d" -o "src/HelloOpenMP.o" "../src/HelloOpenMP.c"
Finished building: ../src/HelloOpenMP.c
Building target: HelloOpenMP
Invoking: MacOS X C Linker
gcc -o "HelloOpenMP" ./src/HelloOpenMP.o
Undefined symbols for architecture x86_64:
"_GOMP_parallel_end", referenced from:
_main in HelloOpenMP.o
"_GOMP_parallel_start", referenced from:
_main in HelloOpenMP.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
make: *** [HelloOpenMP] Error 1
So I guess this was not the right place to add the -fopenmp compiler option? What configuration should I use to build with OpenMP?
Add -fopenmp flag to the linker section as well.
Related
i use eclipse ide for c project on mac computer
i install usblib
sudo brew install libusb
and my program
#include <stdio.h>
#include <stdlib.h>
#include <libusb-1.0/libusb.h>
int main(void) {
libusb_context **libcontext;
int status = libusb_init(libcontext);
if (status == 0) {
printf("success");
}
}
the libusb is at
when i build error
10:17:53 **** Build of configuration Debug for project testusb ****
make all Building file: ../src/testusb.c Invoking: Cross GCC Compiler
gcc -O0 -g3 -Wall -c -fmessage-length=0 -stdlib=libstdc++ -MMD -MP
-MF"src/testusb.d" -MT"src/testusb.o" -o "src/testusb.o" "../src/testusb.c" ../src/testusb.c:16:6: warning: unused variable
'status' [-Wunused-variable]
int status = libusb_init(libcontext);
^ ../src/testusb.c:16:27: warning: variable 'libcontext' is uninitialized when used here [-Wuninitialized]
int status = libusb_init(libcontext);
^~~~~~~~~~ ../src/testusb.c:15:29: note: initialize the variable 'libcontext' to silence this warning
libusb_context libcontext;
^
= NULL 2 warnings generated. Finished building: ../src/testusb.c Building target: testusb
Invoking: Cross GCC Linker gcc -L/opt/local/lib -o "testusb"
./src/testusb.o Undefined symbols for architecture x86_64:
"_libusb_init", referenced from:
_main in testusb.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to
see invocation) make: * [testusb] Error 1
how to fix that?
thanks #Fang suggestion Libusb undefined reference to
i solve the problem.
first type
pkg-config --list-all
query all installed libraries,check libusb whether installed,
then type
pkg-config --libs libusb
link against the libusb i want to use
there should be the output
-lusb
then right click project properties->c/c++ Build->Setting->Cross GCC Linker Miscellaneous,type -lusb-1.0
Today I installed the Allegro game programming library for C and I’ve tried to include one of the header files but when I try to execute gcc -I./include example.c -o a.exe in the terminal, I keep on getting this error:
Undefined symbols for architecture x86_64:
"_main", referenced from:
implicit entry/start for main executable
(maybe you meant: __al_mangled_main)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Any ideas? I installed Allegro 5 using the instructions here: https://wiki.allegro.cc/index.php?title=Install_Allegro5_From_GIT/OSX
example.c code:
#include <stdio.h>
#include <allegro5/allegro.h>
int main(int argc, const char *argv[]){
puts(“Hello, world!”);
return 0;
}
You need to link your executable to Allegro.
According to the FAQ, you should add -lallegro to your compile command, or -lallegro -lallegro_main on OSX
You may need other flags, and Allegro 5 uses pkg-config instead of allegro-config, so do pkg-config allegro-5.0 allegro_main-5.0 --cflags --libs to find out.
You can combine this into a compiler command by using backticks, e.g.
$CC -W -Wall `pkg-config allegro-5.0 allegro_main-5.0 --cflags --libs` foo.c -o foo.exe
I've just started programming in C and decided to use make to build my sample app. Compiling the files using the GCC command works fine, however, using make fails with an error. If make just executes the gcc command under the hood, I don't see why this is even possible.
Here are the list of files:
makefile.make:
app.o: app.c helper.h
gcc -c app.c
helper.o: helper.h helper.c
gcc -c helper.c
app: app.o helper.o
gcc app.o helper.o -o app
app.c
/*
* file: app.c
*/
#include "helper.h"
int main() {
do_something();
return 0;
}
helper.h
/*
* helper.h
*/
void do_something();
helper.c
/*
* file: helper.c
*/
#include <stdio.h>
#include "helper.h"
void do_something() {
printf("Test\n");
printf("Testsss\n");
}
The Problem: Running "make app" throws the error message
Undefined symbols for architecture x86_64:
"_do_something", referenced from:
_main in app.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [app] Error 1
Things Ive tried that works:
Compiling and Linking manually using gcc (using the commands from
make executed serially)
Using "make app.o" and "make helper.o" then running "gcc app.o helper.o -o app" compiles and links the app correctly
rename "makefile.make" to "makefile" or "Makefile". "app.o" and "helper.o" seems to work but i think thats just make doing its default instructions.
I have 3 files, main.c, lists.c, and lists.h.
Im trying to write a Makefile with all the files are in the same directory:
maman21: lists.c lists.h main.c
gcc -g -Wall -ansi main.c -o maman21 -lm
going to the folder through terminal and using make shows me this message:
gcc -g -Wall -ansi main.c -o maman21 -lm
Undefined symbols for architecture x86_64: "_linkedListWay",
referenced from:
_main in main-C9dUT4.o "_reallocWay", referenced from:
_main in main-C9dUT4.o ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to
see invocation)
make: *** [maman21] Error 1
reallocWay and linkedListWay are to functions I'm using in the file.
Thank you for your help.
You've failed to include the lists.c file in the compiler invocation so it doesn't get built.
It should be:
CFLAGS=-g -Wall -ansi
LDLIBS=-lm
maman21: main.o lists.o
main.o: main.c
lists.o: lists.c lists.h
The above uses implicit Makefile rules, it "knows" how to convert a C file to an object (.o) file.
Also, is it normal for Clang to be called gcc?
I'm trying to compile the following libusb snippet on my Mac:
#include <stdio.h>
#include <stdlib.h>
#include <libusb.h>
int main(void) {
libusb_device **devices;
ssize_t device_count = 0;
device_count = libusb_get_device_list(NULL, &devices);
printf("%d devices found\n", (int)device_count);
return EXIT_SUCCESS;
}
I have libusb installed via Homebrew.
I'm getting the following error during compilation:
ld: symbol(s) not found for architecture x86_64
The full compiler output is as follows:
22:28:24 **** Incremental Build of configuration Debug for project libusb ****
make all
Building file: ../src/libusb.c
Invoking: Cross GCC Compiler
gcc -I/usr/local/Cellar/libusb/1.0.9/include/libusb-1.0/ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/libusb.d" -MT"src/libusb.d" -o "src/libusb.o" "../src/libusb.c"
Finished building: ../src/libusb.c
Building target: libusb
Invoking: Cross GCC Linker
gcc -o "libusb" ./src/libusb.o
Undefined symbols for architecture x86_64:
"_libusb_get_device_list", referenced from:
_main in libusb.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [libusb] Error 1
22:28:24 Build Finished (took 119ms)
I understand the problem is to do with the linker not finding the libusb library, right? How do I tell the compiler where that is in Eclipse CDT?
As we worked out in all the comments the link command that worked is
gcc -L/usr/local/Cellar/libusb/1.0.9/lib -o "libusb_example" ./src/libusb_example.o -lusb1.0