I am trying to compile the OpenCV 4.5 library from source on a fresh install of Raspian and I'm running into a problem regarding the C++ standard. After running the cmake command from the build dir, in order to obtain the required makefiles, I get prompted with the message "OpenCV 4.X requires c++11. I tried modifying the CMakeLists.txt adding the set(CMAKE_CXX_STANDARD 11) and also adfding a building flag using the -D CMAKE_CXX_FLAGS='-std=c++11' option but without luck. All options available here: cmake build command + flags I'm not sure how I could get past this and I could use some advice if someone encountered it before, any suggestions? TIA 😃
I'm trying to follow this tutorial to get started with OpenGL: http://www.learnopengl.com/#!Getting-started/Creating-a-window and it requires downloading glfw and CMake.
I have set the downloaded glfw folder as the source code folder and I have created inside that folder another one called "build" which I then set as the build one for the binaries, as the tutorial asks.
I click on "Configure" and I select XCode as the Generator, since I'm on a Mac.
The problem is that when I try to configure the project CMake gives me this error:
The C compiler identification is unknown
CMake Error at CMakeLists.txt:3 (project):
No CMAKE_C_COMPILER could be found.
Configuring incomplete, errors occurred!
See also "/Users/standard/Desktop/glfw-3.2.1/build/CMakeFiles/CMakeOutput.log".
See also "/Users/standard/Desktop/glfw-3.2.1/build/CMakeFiles/CMakeError.log".
I've already read this question, but as far as I can understand, it doesn't have what I need:
CMake error at CMakeLists.txt:30 (project): No CMAKE_C_COMPILER could be found
If you have installed Xcode or Command Line Tools for Xcode, try this:
sudo xcode-select --reset
This happened to me with Xcode10 / Cmake 3.12 after installing Homebrew. Running sudo xcode-select --reset fixed it for me.
Did you install Xcode and Xcode Commandline Tools?
xcode-select --install
If you have Xcode Commandline Tools installed, you should no longer be receiving the xcrun is missing error.
How did you install Cmake? Once you have ensured that Xcode Commandline Tools is installed, please completely remove Cmake from your system and reinstall it. You have a screwed up configuration. There are ways to debug and fix it without a clean install, but since you are new to this, it will be the easiest and lest frustrating way.
Failing that if you do have Xcode Commandline Tools installed, hstdt suggested trying this:
sudo xcode-select --reset
This error means CMake cannot find your standard C/C++ Compiler, looks like you'll need to export the environment variables yourself. you can find the path of your C/C++ compiler with:
xcrun -find c++
xcrun -find cc
Then afterwards when you have the paths, create two variables inside the gui. If you are running it from the cline, it would be something like
cmake -D CMAKE_C_COMPILER="/path/to/your/c/compiler/executable" -D CMAKE_CXX_COMPILER="/path/to/your/cpp/compiler/executable" ...
On a fresh Xcode install the command line tools complain about agreeing to the EULA which build tools don't like. Which you can do with:
sudo xcodebuild -license
If you are on a Mac computer and have Homebrew, you can simply upgrade cmake, forcing the compiler to be reconfigured:
brew upgrade cmake
In my case, I needed to install CMake from CMake official site, download the .dmg, install it and then add the CMake folder the system's PATH.
Before the installation, the output of which cmake is /usr/local/bin/cmake.
After the installation it should be something like /Applications/CMake.app/Contents/bin/cmake.
This has solved the issue for me.
I get exactly this error if ccache is enabled on my machine. Disabling ccache fixed the problem for me.
To check if ccache is enabled, print the systems variables CC or CXX:
echo $CC
echo $CXX
This prints something like the following: ccache clang -Qunused-arguments -fcolor-diagnostics. (CC or CXX are typically overridden by the .bashrc or .zshrc file.)
To disable ccache, use the following:
CC=clang
CXX=clang++
Then rebuild the cmake project:
cmake -G Xcode <path/to/CMakeLists.txt>
Apparently, it is possible to use CMake's Xcode generator also in combination with ccache, as is described here. But I never tried it out myself.
I got this error when I had an invalid value set for CMAKE_OSX_SYSROOT. I was trying to give it the name of the SDK e.g. "macOS 10.13". Setting it to the full path of the SDK resolved the issue.
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk
Compiler detection appears to be broken with Xcode 10 and older versions of CMake. I know that it broke for me with CMake 2.2 and upgrading to the latest (2.13) solved it for me. It was working fine with Xcode 9 and it broke with the upgrade. I tried the other solutions (all good depending on your situation) but upgrading CMake fixed the issue.
If you are on CLion and facing this issue try changing the C and C++ compiler location inside Toolchains settings to the latest one. the default GCC installation directory is /usr/local/Cellar/gcc/...
after I upgrade Xcode to new verison, I met this error, then I upgrade my cmake version, problem solved.
For anyone coming to this question nowadays from google, my problem was fixed via
xcodebuild -runFirstLaunch
I found this by inspecting CMakeFiles/CMakeError.log
(this question similar to this one but is not the same)
I'm using QtCreator on Windows platform, usually with vc toolchain.
sometimes with MinGW-W64, so for now, I'd like to try clang for some reasons.
unlike the post above - I don't use Qt library , just qtcreator as IDE, so I suppose I don't need to re-build it and QtCreator for a using clang kit, is it correct?
there are a few questions about that:
CLang distribution doesn't contain platform or even c/c++ runtime library, should i use it from vc kit? or/and MinGW runtime? how to switch between?
Correct my understanding please if it's wrong - for Win platform, clang has two options to use: 1) normal use - clang.exe ,as on any other platform 2) clang-cl.exe - additional layer which "looks like" cl.exe, and just parses cl command line keys and calls normal clang.
as I understand there is no LLDB for Windows platform , can I use GDB or CDB depends of the used runtime lib and binary format of the executable?
and finally - how to configure all this in qtcreator?
The following steps apply only to MSYS2 64-bit installation of QT Creator 4.5.1 (install instructions here), where you also have MinGW-w64 and mingw32-make installed on MSYS2; and you are building a non-QT C or C++ application.
These instructions use QMake, because QBS doesn't support MSYS2 clang. Well, QMake doesn't support it either, but I did figure out how to add support to QMake and I didn't figure out QBS.
There is QMake support for MSVC-clang but it outputs MSVC makefiles, so you can't build it with MSYS2 make. So that does not apply to us.
Install clang with pacman. I used pacman -Ss mingw-w64-x86_64-clang, your flavour may vary.
Add support for clang to QMake:
In the MSYS2 shell, go into /msys64/mingw64/share/qt5/mkspecs/
Do cp -a win32-g++ win32-clang-msys
Edit win32-clang-msys/qmake.conf and change gcc to clang, and g++ to clang++ (2 places each)
In the same file, take out -fno-keep-inline-dllexport -mthreads which are not supported by clang.
In QT Creator, set up a new Kit:
Go to Manage Kits.
Add a Custom Compiler for C and browse to the installed path (/mingw64/bin/clang.exe under your MSYS2 install).
Add a Custom Compiler for C++ as clang++.exe in the same place)
Add a manual Kit called Clang and set those two compilers as its compilers.
In the manual kit config set "Qt mkspec" as win32-clang-msys
Set "QT Version" to something. Even though I am using a non-QT project, the IDE doesn't like using the kit if "Qt version" is set to None.
Now you can attempt to build your project with the Clang kit and QMake.
I initially tried with QBS and the build failed due to this bug . But the build commands do succeed if I copy-paste them and cut out the bogus -target switch. So for QBS users I guess you have to switch to QMake in the meantime until they fix that bug.
Troubleshooting: I sometimes got an error Project ERROR: failed to parse default search paths from compiler output. This is a problem with QMake's lack of support for clang. The error tended to not occur if I built in a subdirectory of the .pro file, but did occur if I built in a sibling directory.
As a workaround: go back into win32-clang-msys/qmake.conf. Change the first clang back to g++. Then "Run Qmake" (from QT creator or commandline), then change it back. The first time you run QMake it writes the file .qmake.stash and then does not need to generate it again. The contents of this file were bogus for me but building seemed to work anyway.
Undefined references: I found that linking with -static produced a bunch of undefined references to __imp__cxa_ names. Not sure what the problem is here but maybe related to the bug with generating .qmake.stash. I guess the Qt developers would need to officially add non-MSVC Clang support to QMake.
Multiple definitions: The CLang linker gave multiple definitions for inline DLLexport functions. I found no workaround yet for this; g++ has -fno-keep-inline-dllexport to avoid this problem but CLang 5 does not support that flag.
I am using ubuntu 14.04, cmake 2.8.12.2, Qt5.6.2 (a built version), GNU make 3.81
After I run cmake with cmake PathToSource -G "Eclipse CDT4 - Unix Makefiles"
I do make. I get #error "You must build your code with position independent code if Qt was built with -reduce-relocations. " "Compile your code with -fPIC (-fPIE is not enough)."
# error "You must build your code with position independent code if Qt was built with -reduce-relocations. "\
I then download source file of Qt5.7.0, build and install it without problem. I do again cmake PathToSource -G "Eclipse CDT4 - Unix Makefiles", make it. I get many errors, such as /home/sflee/Documents/Software_dev/3rd_party/Qt5.7.0/include/QtCore/qhash.h:957:10: error: ‘pair’ does not name a type
auto pair = qAsConst(*this).equal_range(akey); and /home/sflee/Documents/Software_dev/3rd_party/Qt5.7.0/include/QtCore/qbasicatomic.h:285:14: error: ‘Ops’ has not been declared
{ return Ops::fetchAndAddRelease(_q_value, valueToAdd); }
How to solve it?
Qt 5.7 requires C++11 compiler. If you get that kind of error from auto pair, it sounds like your compiler is not compiling C++11 code. There are two possible reasons:
You just need to pass -std=c++11 to your compiler, as explaned under this question.
You have too old compiler. However, since you compiled Qt 5.7 itself with the same compiler, this shouldn't be the problem for you.
Edit/Update/Note: Just let clang use libstdc++. Has been working really well for me so far.
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In the past I have been able to succeed by doing something with cmake, but just now I discovered a buildit script inside the lib directory of the http://llvm.org/svn/llvm-project/libcxx/trunk project tree.
This buildit script appears to not make use of libsupc++ which is what the cmake approach that I took earlier used. For instance, this guide shows one cmake incantation to produce a makefile for libc++, which will be able to take care of compiling and installation.
My question is what is the difference between these different ways to produce the LLVM-libc++ and which one should be used? Will they behave differently?
The buildit script does not appear to provide any help for installation. Are there directions anywhere for how to properly install the library? With my previous libc++ built with cmake, I had to always add -lc++ to the linker flags (and the path with -L), which is not necessary in my OS X makefiles.
The libc++ website has a nice overview of the possible ways to build libc++.
I suggest using CMake + libc++abi.
Also see the Arch Linux User Repository build script, which uses the buildit script. I installed libc++ from that and used it with the Arch Linux Clang package succesfully by using
clang++ -std=c++11 -stdlib=libc++ -lc++abi