From the research I have done, the problem seems to be with clang. If that is the case, how would I fix this on a Mac? Would switching to Ubuntu/Linux be a better option?
I'm not sure if it is relevant, but my professor is having us code using C syntax using g++ and saving our files as '.cpp' before we dive into C++.
Warning:
clang: warning: argument unused during compilation: '-ansi'
[-Wunused-command-line-argument]
Makefile:
CC = g++
calendar: main.o calendar.o appt.o day.o time.o
$(CC) main.o calendar.o appt.o day.o time.o -g -ansi -Wall -o calendar.out
%.o: %.cpp
$(CC) -Wall -c $<
You are correct in believing that this warning is issued by clang++ in these
circumstances and not by g++, and that you see it on your Mac because g++ is
really clang++.
The GCC option -ansi is meaningful for compilation and not meaningful
for linkage. Clang is warning you because you are passing it in your linkage recipe:
$(CC) main.o calendar.o appt.o day.o time.o -g -ansi -Wall -o calendar.out
where it is ineffective, and not passing it to your compilation recipe:
$(CC) -Wall -c $<
The wording of the diagnostic is misleading since it is provoked here
precisely by the absence of compilation. Nevertheless, it does
draw attention to a mistake on your part. Remove -ansi from your linkage recipe and add it to your compilation recipe.
Related
CC=g++
CFLAGS=-O3 -c -Wall
DFLAGS=-g -Wall
LDFLAGS= -lz -lm -lpthread
KSWSOURCE=ksw.c
ALGNSOURCES=main.cpp aligner.cpp graph.cpp readfl.cpp hash.cpp form.cpp btree.cpp conLSH.cpp
INDSOURCES=whash.cpp genhash.cpp formh.cpp conLSH.cpp
INDOBJECTS=$(INDSOURCES:.cpp=.o) $(KSWSOURCE:.c=.o)
ALGNOBJECTS=$(ALGNSOURCES:.cpp=.o) $(KSWSOURCE:.c=.o)
INDEXER=conLSH-indexer
ALIGNER=conLSH-aligner
all: $(INDSOURCES) $(ALGNSOURCES) $(KSWSOURCE) $(ALIGNER) $(INDEXER)
$(ALIGNER): $(ALGNOBJECTS)
$(CC) $(ALGNOBJECTS) -o $# $(LDFLAGS)
$(INDEXER): $(INDOBJECTS)
$(CC) $(INDOBJECTS) readfl.o -o $# $(LDFLAGS)
debug:
$(CC) $(DFLAGS) $(ALGNSOURCES) $(KSWSOURCE) $(LDFLAGS)
.cpp.o:
$(CC) $(CFLAGS) $< -o $#
.c.o:
$(CC) $(CFLAGS) $< -o $#
clean:
rm -rf *.o $(ALIGNER) $(INDEXER) a.out
I have the above makefile but I am getting an error
/usr/lib/gcc/i686-linux-gnu/4.8/include/emmintrin.h:31:3: error: #error "SSE2 instruction set not enabled"
# error "SSE2 instruction set not enabled"
From what I understand and googled this is a flag for parallel computation.
I tried from other posts with the same problem to either include:
CXXFLAGS=-03 -c Wall -mfpmath=sse
OR:
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -msse -msse2 -msse3")
but without any success. Can you help?
I am not sure a CXX flags is necessary because a lot of (probably) cascading errors are shown in ksw like,
ksw.c:49:2: error: ‘__m128i’ does not name a type
__m128i *qp, *H0, *H1, *E, *Hmax;
-msse2 is the specific option, so passing that to GCC will work, if you get your build scripts set up to actually do that. https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html#x86-Options
Or better, use -march=native to enable everything your CPU has, if you're building for local use, not for distributing a binary that might have to work on an old-but-not-ancient CPU. (Of course, if you care about performance, it's weird to be building for 32-bit mode. SSE2 is baseline for x86-64. Unless your CPU is too old to support SSE2, e.g. a Pentium III. Or for example, there are embedded x86 CPUs without SSE, like AMD Geode. In that case, a binary built (successfully) with -msse2 will probably crash with an illegal instruction on such a CPU.)
-mfpmath=sse just tells GCC to use SSE for scalar FP math assuming that SSE is available; unrelated to telling GCC to assume the target CPU does support SSE2. It can be good to use it as well for performance, but it's not going to matter in getting your code to compile.
And yes, SSE1/2 intrinsic types like __m128i will only get defined when SSE is enabled, so error: ‘__m128i’ does not name a type is a clear sign that -msse wasn't enabled
If using autoconf or something, maybe use this:
./configure CPPFLAGS="-O3 -march=native -fno-math-errno"
If you have .c files as well as .cpp, set CFLAGS as well as CPPFLAGS. More options like -flto can be helpful for optimization (cross-file inlining at link time), if you get those added to your LD options. As well as any other optimization options like -ffast-math if you want to use it. Or at least -fno-trapping-math helps some, and GCC already did optimizations that violated the semantics trapping-math was supposed to provide. See this Q&A re: -fno-trapping-math -fno-math-errno being safe to use basically everywhere, even in code that depends on strict FP like Kahan summation.
This worked for me also:
./configure CPPFLAGS="-march=native"
If I compile in two stages, using a particular language standard:
g++ -std=c++2a -c file1.cpp #compile source files
g++ -std=c++2a -c file2.cpp
g++ -std=c++2a file1.o file2.o -o program #link 'em
...can I leave the -std=c++2a out of the link command, or is it sometimes needed?
Version is gcc 10.
I guess you are compiling on Linux with a recent GCC. Be sure to read more about C++ and about your particular compiler (i.e. GCC 9 is not the same as GCC 10). Check with g++ --version what it is.
In practice you want to compile with warnings and debug information (in DWARF for GDB inside your ELF object files and executables), so use
g++ -std=c++2a -Wall -Wextra -g -c file1.cpp
and likewise for file2.cpp
Later (once your program is correct enough, e.g. has few bugs) you could want to ask the compiler to optimize it. So you could use
g++ -std=c++2a -Wall -Wextra -O3 -g -c file1.cpp
Practically speaking, you'll configure your build automation tool (e.g. GNU make or ninja) to run your compilation commands.
In rare cases, you could want to use link time optimizations. Then you need to both compile and link with g++ -std=c++2a -Wall -Wextra -O3 -g -flto and perhaps other options.
Be aware that link time optimization could almost double your build time.
You could also be interested by static analysis options of GCC 10 (or even by writing your own static analysis using GCC plugins).
I'm building a shared library and an application using that lib on Cygwin. With GCC CMake creates a .dll.a to use when linking. Switching to clang I get
[ 34%] Built target xxx_shared
make[2]: *** No rule to make target 'src/libxxx.dll.a', needed by 'xxx.exe'. Stop.
Is this a bug in the clang CMake extension?
I'm using cmake --version 3.3.2
Yes, it seems to be a bug in CMake. Running make VERBOSE=1 reveals that with GCC:
/usr/bin/c++.exe -g -shared -Wl,--enable-auto-import -o XXX -Wl,-Bstatic -lm -Wl,-Bdynamic -lstdc++ -lcygwin -ladvapi32 -lshell32 -luser32 -lkernel32
while with clang:
/usr/bin/clang++ -fPIC -g -shared -o XXX -Wl,-Bstatic -lm -Wl,-Bdynamic -lstdc++ -lcygwin -ladvapi32 -lshell32 -luser32 -lkernel32
So it seems that somehow clang++ does not get the -Wl,--enable-auto-import flag. Manually running the corrected clang++ command correctly creates the expected .dll.a allowing the rest of the build to proceed as expected.
Haven't figured out why this happens yet, though. At this point I can't decipher CMakes platform extensions, which seems to set this for GCC.
Update: I've reported this here.
I'm trying to link a really simple GLES2 & EGL program using g++ 4.9.1, on a Ubuntu Trusty system. I'm using the mesa libraries.
I'm getting linker errors for EGL functions:
test.cpp:(.text+0x342): undefined reference to `eglGetDisplay'
test.cpp:(.text+0x389): undefined reference to `eglInitialize'
test.cpp:(.text+0x40f): undefined reference to `eglCreateContext'
test.cpp:(.text+0x458): undefined reference to `eglCreatePbufferSurface'
test.cpp:(.text+0x49e): undefined reference to `eglMakeCurrent'
I am compiling test.cpp with
g++ -std=c++0x -Wall -Werror -lEGL -lGLESv2 -o test test.cpp
I've tried switching the order of libraries, which sometimes matters, but I get the same problem. Is there a library I'm missing here?
I've run readelf -Ws /usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so and all of the required functions are defined.
You should put libraries to the end of a command line
g++ -std=c++0x -Wall -Werror -o test test.cpp -lEGL -lGLESv2
I managed to fix this by compiling the C++ file to an object file, and then linking as a separate step. I'm not sure why this works, when the one-line compilation doesn't.
g++ -std=c++0x -Wall -Werror -c -o test.o test.cpp
g++ -o test test.o -lGLESv2 -lEGL
I've put the question to the community to try to figure out why: Single-command compile and link fails, separate steps work
My code is as simple as this:
#include <mpi.h>
int main(int argc, char**args) {
MPI_Init(&argc, &args);
int mpiSize;
int mpiRank;
MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
MPI_Finalize();
}
I first compile it to object file:
g++ -c src/mpitest.cpp -o src/mpitest.o
Then I can easily use mpicxx:
mpicxx src/mpitest.o -o mpi
But I want to use g++ instead, because It's easier for automake, so I tried:
mpicxx src/mpitest.o -o mpi -show
It prints out:
g++ src/mpitest.o -o mpi -I/usr/local/include -L/usr/local/lib -L/usr/local/lib -lmpichcxx -lmpich -lopa -lpthread -lrt
And yes, that command actually does the same thing successfully. However, If I tried to change it to (I just change the object file and output to the end):
g++ -I/usr/local/include -L/usr/local/lib -L/usr/local/lib -lmpichcxx -lmpich -lopa -lpthread -lrt src/mpitest.o -o mpi
Which is what automake does when it adds LDFLAGS, the g++ start complaining...
src/mpitest.o: In function `main':
..src/mpitest.cpp:5: undefined reference to `MPI_Init'
../src/mpitest.cpp:8: undefined reference to `MPI_Comm_size'
../src/mpitest.cpp:9: undefined reference to `MPI_Comm_rank'
../src/mpitest.cpp:10: undefined reference to `MPI_Finalize'
collect2: ld returned 1 exit status
What happens with g++ ? I couldn't figure out. Please enlighten me. Why the order here matter at all ? What is the proper way to do what I want from the beginning ?
Thanks a lot
p/s : g++ --version
g++ (Ubuntu 4.4.3-4ubuntu5) 4.4.3
mpi is mvapich2
I didn't really remember, maybe since version 4, library to link with -l must be passed after all source and object files.