I am trying to build cmake source, which requires C++11.
The build halts and apparently the complaint is that C++11 is not detected. The g++ mode is actually set to -std=gnu++17
This is part of the console log
---------------------------------------------
CMake 3.18.20200919, Copyright 2000-2020 Kitware, Inc. and Contributors
Found GNU toolchain
C compiler on this system is: gcc
C++ compiler on this system is: g++ -std=gnu++17
Makefile processor on this system is: make
g++ has setenv
g++ has unsetenv
g++ does not have environ in stdlib.h
g++ has stl wstring
g++ has <ext/stdio_filebuf.h>
---------------------------------------------
g++ -std=gnu++17 -DCMAKE_BOOTSTRAP -DCMake_HAVE_CXX_MAKE_UNIQUE=1 -c $HOME/Apps/CMake-master/Source/cmAddCustomCommandCommand.cxx -o cmAddCustomCommandCommand.o
This is part of the error in the log file...
In file included from /usr/include/c++/5/unordered_map:35:0,
from cmake_bootstrap_11920_test.cxx:4:
/usr/include/c++/5/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
#error This file requires compiler and library support \
^
cmake_bootstrap_11920_test.cxx:7:2: error: #error "Compiler is not in a mode aware of C++11."
#error "Compiler is not in a mode aware of C++11."
^
cmake_bootstrap_11920_test.cxx:70:16: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
int Member = 1;
Looking around on the web, I noticed that C++11 is only available after gcc version 4.6.
I checked my version, and it seems to be above.
g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609
I understand the -std=c++11 flag is used to enable the C++11 features in g++, but I don't seem to know what I am doing in this case.
I tried editing the CompileFlags.cmake file, but no change occurs.
I came upon this page which points to the cmake source I am using.
It says...
bootstrap: Require compiler mode aware of C++11
Some compilers have enough features enabled in their default modes to
pass our simple C++11 unique_ptr check but do not enable enough to build
CMake. Poison this case so that we choose one of the explicit `-std=`
options for such compilers.
Not sure what that means exactly.
How exactly do I change the g++ mode, to C++11, so that on running the bootstrap command, C++11 is used?
Or, in other words, how do I change std to point to C++11 (-std=c++11)?
First of all, you have g++ version 5.4.0 in your host PC installed, which is good, cause it means this is also supports the C++11, which you want to use.
To set it up, you could define it in your CMakeList.txt file:
set (CMAKE_CXX_STANDARD 11)
that should do the trick.
Please also check the documentation:
https://cmake.org/cmake/help/v3.1/variable/CMAKE_CXX_STANDARD.html
Usually, I would suggest to use the latest standard that you compiler is supporting (https://gcc.gnu.org/projects/cxx-status.html), cause you'll get also the latest features introduced in that standard. Exception for this rather in case you are working with legacy codes.
Related
I'm trying to build my program using gcc 5 with c++11 enabled.
My makefile calls gccmakedep which then complains about missing c++11 support:
error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options. #error This file requires compiler and library support \
I modified the line in the makefile to set the required option:
gccmakedep -- -std=gnu++11 -- $(SRCS)
It doesn't work. I get the same error. I think gccmakedep doesn't recognize the option.
How can I solve this?
I'm using the Windows version of Clang (LLVM) 8 under Windows.
I'm compiling a code which uses OpenMP.
Under the lib folder of Clang there are 2 files which are OpenMP related:
libomp.lib.
libiomp5md.dll.
My questions are:
When I compile the code I use the flags -Xclang -fopenmp for the compiler. In in GCC and ICC using the flags tell the compiler to link the OpenMP library automatically. What about Clang? Does it do it automatically or must I link with libomp.lib manually? Is there a way to trigger automatic linking to the OpenMP library?
Answer: This was answered in Michael Klemm's answer below - Use the clang driver both for compiling and linking and then the -fopenmp will work as in GCC.
When I link with libomp.lib manually (Defining as a library for the linker) the output exe requires libomp.dll while the supplied OpenMP Dynamic Library is libiomp5md.dll. Is that a bug or is it because I link manually?
Answer: The libomp.dll is supplied in the bin folder and not the lib folder.
What's the proper way to utilize OpenMP in Clang under Windows? The clang-cl driver doesn't work with /openmp or -openmp as the MSVC's cl compiler.
Answer: Currently it can be done either with clang -fopenmp ..., clang-cl -Xclang -fopenmp ... or clang-cl /clang:-fopenmp ... (Which is equivalent of -Xclang -fopenmp).
Remark
On Windows I use Windows Driver of Clang using clang-cl.
Adding clarity to what the OpenMP libraries actually are, and how to use them on Windows with clang-cl
libomp.dll and libiomp5md.dll ARE THE SAME FILES!
When compiling for Windows, you link against libomp.lib OR libiomp5md.lib which will link to the same-named DLL at runtime, i.e. libomp.dll OR libiomp5md.dll respectively.
If you load 2 files that use the "different-name DLL," the interpreter will crash and give you a nasty error like: OMP: Error #15: Initializing libiomp5md.dll, but found libomp.dll already initialized.
Why? Because the program has no idea they are the same DLL, they have different names, so it assumes they are different. And it crashes. For this reason only, you can choose to swap which OpenMP DLL you link to in your program.
If your program doesn't crash and give you an error, you can keep using the same link to OpenMP. Otherwise, to silence the error, link to the one that is loaded by another program already.
If using clang-cl.exe which is the "drop-in" Clang replacement for MSVC cl.exe you should pass a compiler argument such as -Xclang -fopenmp which will convert the argument over to "Clang language." Don't forget to still pass to the linker the OpenMP LIB you chose, because on Windows, it won't be automatic.
That's all I've learned as brief as possible about OpenMP linking on Windows.
To compile and link OpenMP code with clang on Windows, you will have to pass -fopenmp to both the compiler and the linker:
clang -fopenmp -o bla.obj -c bla.c
clang -fopenmp -o bla.exe bla.obj
I am currently trying to compile libxml2 on Solaris. When I run the ./configure script provided with the sources, the gcc and g++ compilers are automatically used. However, I would like to use cc and CC compilers. So I run :
./configure CC=cc CXX=CC
It works but then, when I run "make", I get some errors which prevent the libraries to be generated.
When gcc and g++ are used, everything goes well with no errors, so I was wondering: can I use the librairies generated with gcc/g++ the same way I would have used them if I had successively generated them with cc/CC?
What are the differences between a lib generated with cc and the same lib generated with gcc on Solaris?
You can use either the gcc or cc C compilers pretty much interchangeably.
You can mix the g++ and CC C++ compilers in certain ways, but only on x86 Solaris and if your CC compiler is new enough to have the -compat=g option available.
The GNU g++ and the Solaris Studio CC C++ compilers default to completely different ABIs and C++ run-time libraries. On x86 Solaris platforms, newer versions (since version 12.?, if I remember correctly) provide a -compat=g option to use the g++ ABI and run-time libraries. The Studio 12.4 CC compiler adds a -std=v option to select different versions of the g++ or Sun C++ ABI and run-time libraries:
c++03 (zero-3, not oh-3)
Equivalent to the -compat=g option. It selects C++ 03 dialect and g++ ABI; it is binary compatible with g++ on Solaris and Linux It
sets the __SUNPRO_CC_COMPAT preprocessor macro to 'G'.
c++11
Selects C++ 11 dialect and g++ binary compatibility. It sets the __SUNPRO_CC_COMPAT preprocessor macro to 'G'.
c++0x (zero-x, not oh-x)
Equivalent to c++11.
and
The -std=c++03 provides compatibility with the gcc/g++ compiler on
all Oracle Solaris and Linux platforms.
With -std=c++03, binary compatibility extends only to shared
(dynamic or .so) libraries, not to individual .o files or archive (.a)
libraries. The gcc headers and libraries used are those provided with
the compiler, rather than the version of gcc installed on the system.
Note that the Studio 12.4 CC compiler uses the g++ headers and libraries supplied bundled with the CC compiler itself. 12.3 and earlier use the g++ headers and libraries installed on the system under /usr/sfw.
On SPARC Solaris, you have to use either g++ or CC for the entire application.
I've recently downloaded CUDA 7 and set it up to work with my project. On Mac, CUDA 7 requires clang to be the host compiler.
Now, I'm using a number of C++11 features. I've enabled these with -std=c++11 passed to nvcc this works. However, if I pass -Xcompiler -std=c++11 to nvcc, I get the following error regardless of if I also passed -std=c++11 by itself. The error is:
"invalid argument '-std=c++11' not allowed with 'C/ObjC'"
It seems like this should work, it certainly does with GCC. Anyone have a workaround. Otherwise, I'll file a bug report with Nvidia.
nvcc -dryrun ... will show what commands nvcc will execute. I don't currently have access to CUDA 7, only 6.5, but mine issues, among other things, two commands that compiles generated C source. This code generated by cudafe and have to be compiled by C compiler, but -Xcompiler adds options for both C and C++ modes.
I guess difference with my gcc situation is that I'm getting a warning while you have an error (this is exactly how gcc and clang differs in that case). For both compilers I don't see any way to suppress it, so I guess you have to fix your .cmake files to omit -Xcompiler options. This options shouldn't be used for language standard, just some very compiler-specific things.
Of course it doesn't work. You are specifying C++ options while using a C or Objective-C compiler. The source files must be C++ or Objective-C++.
std::chrono ought to be supported in g++ 4.8.*. However, when I try to compile using it using g++ 4.8.3, it cannot find various declarations. I am, of course, using -std=c++11.
For example this invocation (from an autogenerated file; that's why the -std appears twice):
g++-4.8 -g -msse2 -m64 <defines> <warnings> -std=c++11 -fexceptions -std=c++11 <includes'-path> -c <source-file.cpp> -o <out-path>
Produces this error:
<source-file, line>: error: ‘std::chrono::monotonic_clock’ has not been declared
I wasn't able to find very much that wasn't immediately a compiler version or missing -std=c++11. By inference from this, I shouldn't need anything else.
Question: what's wrong, how do I fix it?
There is no std::chrono::monotonic_clock in standard C++. There is a std::chrono::steady_clock, however.
In fairness to Microsoft - and burritos everywhere - there was a monotonic_clock in the working drafts during the development of C++11 which was replaced by steady_clock.
It seems to me that you could use code like this to determine whether you're using an old library implementation (that provides monotonic_clock but not steady_clock) or a new one (that provides steady_clock but possibly not monotonic_clock).
#if defined(__GLIBCXX__) && (__GLIBCXX__ < 20120322)
typedef std::chrono::monotonic_clock steady_clock;
#else
typedef std::chrono::steady_clock steady_clock;
#endif
The datestamp above corresponds to the libstdc++ shipped with GCC 4.7.0, according to GNU. I'd welcome any improvements or corrections to this code, for example to support libraries other than libstdc++.