Catalina C++: Using <cmath> headers yield error: no member named 'signbit' in the global namespace

Question

After upgrading to Catalina from Mojave, Setuping: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk in the env.

I'm unable to compile a program that use <cmath> header.

I tried changing CFLAGS, CCFLAGS, CXXFLAGS to point to the MacOSSDK Location that change nothing

Scanning dependencies of target OgreMain
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f OgreMain/CMakeFiles/OgreMain.dir/build.make OgreMain/CMakeFiles/OgreMain.dir/build
[  0%] Building CXX object OgreMain/CMakeFiles/OgreMain.dir/src/OgreASTCCodec.cpp.o
cd /Users/roman/Downloads/ogre-1.12.2/build/OgreMain && /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++  -DOgreMain_EXPORTS -D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES=0 -I/Users/roman/Downloads/ogre-1.12.2/OgreMain/src/OSX -I/Users/roman/Downloads/ogre-1.12.2/OgreMain/include/Threading -I/Users/roman/Downloads/ogre-1.12.2/OgreMain/src -I/Users/roman/Downloads/ogre-1.12.2/build/Dependencies/include -I/Users/roman/Downloads/ogre-1.12.2/OgreMain/include -I/Users/roman/Downloads/ogre-1.12.2/build/include -I/Users/roman/Downloads/ogre-1.12.2/OgreMain -isystem /usr/local/include  -Wall -Winit-self -Wcast-qual -Wwrite-strings -Wextra -Wundef -Wmissing-declarations -Wno-unused-parameter -Wshadow -Wno-missing-field-initializers -Wno-long-long -Wno-inconsistent-missing-override  -msse -O3 -DNDEBUG -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -fPIC -fvisibility=hidden -fvisibility-inlines-hidden   -std=c++11 -o CMakeFiles/OgreMain.dir/src/OgreASTCCodec.cpp.o -c /Users/roman/Downloads/ogre-1.12.2/OgreMain/src/OgreASTCCodec.cpp
In file included from /Users/roman/Downloads/ogre-1.12.2/OgreMain/src/OgreASTCCodec.cpp:29:
In file included from /Users/roman/Downloads/ogre-1.12.2/OgreMain/src/OgreStableHeaders.h:40:
In file included from /Users/roman/Downloads/ogre-1.12.2/OgreMain/include/OgrePrerequisites.h:309:
In file included from /Users/roman/Downloads/ogre-1.12.2/OgreMain/include/OgreStdHeaders.h:10:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath:314:9: error: no member named 'signbit' in the global namespace
using ::signbit;
      ~~^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath:315:9: error: no member named 'fpclassify' in the global namespace
using ::fpclassify;
      ~~^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath:316:9: error: no member named 'isfinite' in the global namespace; did you mean 'finite'?
using ::isfinite;

for example the macro: isless is present in the global namespace and on my computer:

➜ cat math.h | grep "isless"

#define isless(x, y) __builtin_isless((x),(y))
#define islessequal(x, y) __builtin_islessequal((x),(y))
#define islessgreater(x, y) __builtin_islessgreater((x),(y))
➜  pwd
/usr/local/include
➜

Even the cmath header include it:

➜ cat /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath | grep "math.h"
#include <math.h>

And my command line have the option -isystem /usr/local/include

This should work...

Solution 1

I'm curious: What compiler are you using? What's the value of CMAKE_OSX_SYSROOT?

I'm fairly convinced this is the result of a wrong CMAKE_OSX_SYSROOT. I had the problem you're describing when using python bindings for clang (where CMake doesn't manage the compiler call), but I managed to recreate the error in CMake by doing:

set(CMAKE_OSX_SYSROOT "")  # Reset.

I solved my problem by following the answers to this question: Cannot compile R packages with c++ code after updating to macOS Catalina.

To summarise: On Catalina, /usr/include is purged and protected by SIP. Thus, any project that expects the C headers to be found there will fail to compile. If I remember correctly, Apple recommends to file bug reports to projects that expect C headers in /usr/include.

You must point the build system of the code you're trying to compile to the right headers:

(1) Make sure Xcode is up to date. There's no telling what an outdated Xcode on Catalina might do to your build environment.

(2) Use the -isysroot /sdk/path compiler flag, where /sdk/path is the result of xcrun --show-sdk-path. I'm not sure what CMake's best practice is, but try doing

set(CMAKE_OSX_SYSROOT /sdk/path)

or

set(CMAKE_CXX_FLAGS "[...] -isysroot /sdk/path")

If that solves the problem, you may want to look for a better way to do this in CMake.

Of course, if you're adventurous, you could also disable SIP, as suggested in the answer to my question: /usr/include missing on macOS Catalina (with Xcode 11)

Solution 2

Using the command:

gcc -Wp,-v -E -

my #include <...> search sequence:

/usr/local/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/System/Library/Frameworks (framework directory)

The reason of #include error is described below:

• #include<cmath> resides in /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1
• It includes <math.h>.
• It searches /usr/local/include directory as this is the first directory to search. There is a math.h in /usr/local/include/c++/9.3.0/ directory
• It tries to use this.
• But expectation was to use the math.h of the same directory /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1
• The math.h of /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1 include math.h of /usr/local/include using #include_next<math.h>
• As wrong math.h is included/linked with /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/cmath, the compilation error happens

The fix:

1. If we can alter the search order of #include<...> to search /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1 at first, it can be fixed.

2. Using #include</Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/math.h> instead of <math.h> in /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/cmath

I have followed the #2 option and build is successful now!

And thanks to solodon for the detailed answer. I followed the answer to fix the issue.

Solution 3

You may try to use the CommandLineTools SDK rather than the XCode.app SDK.

I fix this problem when I compiling PointCloudLibrary (PCL)

#Check the current sdk
xcrun --show-sdk-path

#Change sdk
sudo xcode-select -s /Library/Developer/CommandLineTools          #Using CommandLineTools SDK
sudo xcode-select -s /Applications/Xcode.app/Contents/Developer   #Using XCode.app SDK

Also, reinstall XCode.app and CommandLineTools may help.

Solution 4

I am having the same problem while trying to target iOS (both on my MacBook Air and on GitHub Actions runner) and here are a few more thoughts on the problem even though I'm not familiar enough with Apple's ecosystem to suggest a proper solution. The original command line was coming from CMake in cpprestsdk, but once I boiled it down to essentials, here is a short repro.

1. Create file cmath-bug.cpp with the only line in it:

    #include <cmath>

2. Run (newlines in front of some arguments are for reading convenience, remove them)

clang -v -x c++ -target arm64-apple-ios13.2 -fcolor-diagnostics -std=c++11 -stdlib=libc++ 
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk 
-isystem  /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include
-c cmath-bug.cpp

When I run it, i get the familiar to many facing the same issue:

Apple clang version 11.0.0 (clang-1100.0.33.16)
Target: arm64-apple-ios13.2
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple arm64-apple-ios13.2.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name cmath-bug.cpp -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables -target-sdk-version=13.2 -target-cpu cyclone -target-feature +fp-armv8 -target-feature +neon -target-feature +crypto -target-feature +zcm -target-feature +zcz -target-feature +sha2 -target-feature +aes -target-abi darwinpcs -fallow-half-arguments-and-returns -dwarf-column-info -debugger-tuning=lldb -ggnu-pubnames -target-linker-version 530 -v -coverage-notes-file /Users/myuser/Projects/C++/cmath-bug.gcno -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk -isystem /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include -stdlib=libc++ -internal-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1 -Wno-framework-include-private-from-public -Wno-atimport-in-framework-header -Wno-extra-semi-stmt -Wno-quoted-include-in-framework-header -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/myuser/Projects/C++ -ferror-limit 19 -fmessage-length 204 -stack-protector 1 -fstack-check -mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=ios-13.2.0 -fcxx-exceptions -fexceptions -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o cmath-bug.o -x c++ cmath-bug.cpp
clang -cc1 version 11.0.0 (clang-1100.0.33.16) default target x86_64-apple-darwin19.0.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include/c++/v1"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/Library/Frameworks"
ignoring duplicate directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include"
#include "..." search starts here:
#include <...> search starts here:
 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/System/Library/Frameworks (framework directory)
End of search list.
In file included from cmath-bug.cpp:1:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath:318:9: error: no member named 'signbit' in the global namespace
using ::signbit;
      ~~^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath:319:9: error: no member named 'fpclassify' in the global namespace
using ::fpclassify;
      ~~^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cmath:320:9: error: no member named 'isfinite' in the global namespace; did you mean 'finite'?
using ::isfinite;
      ~~^

The only 2 include directories I pass on my original command line exist and are:

$ ls -alF /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk
lrwxr-xr-x  1 root  wheel    12B Dec 17 11:54 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk@ -> iPhoneOS.sdk
$ ls -alF /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include
total 2160
drwxr-xr-x  169 root  wheel   5.3K Dec 17 12:07 ./
drwxr-xr-x    5 root  wheel   160B Nov  4 19:22 ../
 ...
-rw-r--r--    9 root  wheel    32K Nov  4 19:52 math.h
 ...

But the interesting bits here are the non-existing include directories it reports as well as the include directories it ends up searching eventually and their order. My guess is that additional directories not mentioned on the command line are inserted by Apple Clang's driver based on some Apple-specific logic.

You can see from the reported error that the <cmath> header is found at: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/cmath and at line 304 of it you can see:

#include <__config>      // Line 304
#include <math.h>        // This one ends up causing troubles
#include <__cxx_version>

Judging from the fact that in that same folder /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/ there is a file math.h that provides the necessary definitions, e.g.:

#include <__config>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

#include_next <math.h>

#ifdef __cplusplus

// We support including .h headers inside 'extern "C"' contexts, so switch
// back to C++ linkage before including these C++ headers.
extern "C++" {

#include <type_traits>
#include <limits>

// signbit

#ifdef signbit

template <class _A1>
_LIBCPP_INLINE_VISIBILITY
bool
__libcpp_signbit(_A1 __lcpp_x) _NOEXCEPT
{
    return signbit(__lcpp_x);
}

#undef signbit

template <class _A1>
inline _LIBCPP_INLINE_VISIBILITY
typename std::enable_if<std::is_floating_point<_A1>::value, bool>::type
signbit(_A1 __lcpp_x) _NOEXCEPT
{
    return __libcpp_signbit((typename std::__promote<_A1>::type)__lcpp_x);
}

...

#elif defined(_LIBCPP_MSVCRT)
...
#endif  // signbit

the authors of <cmath> were expecting the math.h from that same folder be included first and then the #include_next <math.h> directive find the system-specific math.h. That is not what's happening in reality however.

If you look at the first 2 entries in searched directories:

#include <...> search starts here:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1

you see that system-specific include directory ends up being above the Clang-injected standard library directory, which is why the system-specific math.h is being found, not the one in the same folder as the rest of the standard library headers. This is likely the case because if I explicitly add the standard library include directory to my command line BEFORE the other two directories -isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1 the problem goes away and I am able to compile the file. That's not what Clang's driver or whatever else is involved here does automatically: it adds that standard library directory via -internal-system (not sure what's the semantics of that internal flag) and it adds it AFTER the system directory.

Now if you look at the list of ignored directories, the very first entry in that list is:

ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk/usr/include/c++/v1"

of which the trailing c++/v1 part does not exist on my machine, making me wonder whether the iPhone SDK installation was supposed to create a symbolic link c++ inside the existing part of the path to point to /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++ directory to make the whole thing work.

Anyways, this what I think is happening and I wonder if anyone knows how to properly fix this?

Thank you!

P.S. For the context:

$ xcode-select -p
/Applications/Xcode.app/Contents/Developer
$ xcrun --show-sdk-path -sdk iphoneos13.2
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk

Solution 5

It is possible your copy of Xcode is corrupted. Check with codesign:

codesign --verify /Applications/Xcode.app

This happened to me, and the problem was corrupted Xcode. Reinstalling fixed it.

Something had modified the following:

file added: /Applications/Xcode-11.3.1-.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.7/lib/python3.7/json/__pycache__/scanner.cpython-37.pyc
file added: /Applications/Xcode-11.3.1-.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.7/lib/python3.7/json/__pycache__/decoder.cpython-37.pyc
file added: /Applications/Xcode-11.3.1-.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.7/lib/python3.7/json/__pycache__/encoder.cpython-37.pyc
file added: /Applications/Xcode-11.3.1-.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.7/lib/python3.7/json/__pycache__/__init__.cpython-37.pyc
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS.sdk/usr/include/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/WatchOS.platform/Developer/SDKs/WatchOS.sdk/usr/include/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/Kernel.framework/Versions/A/Headers/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/DriverKit19.0.sdk/System/DriverKit/usr/include/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/WatchSimulator.platform/Developer/SDKs/WatchSimulator.sdk/usr/include/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator.sdk/usr/include/math.h
file modified: /Applications/Xcode-11.3.1-.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/include/math.h

math.h was empty in all the above places.

View more solutions

Comments

[Eljay]

Does xcode-select -p match where Xcode is located? Can you change the code to using std::signbit;, likewise for the others? Are you compiling as C++11 or later?

[roman Sztergbaum]

Compiling as C++ 11. I cannot change the code, it's an external dependencies ! yes xcode-select -p match where XCode is located.

[Eljay]

That's not good. The code is trying to do using ::signbit; and the symbol isn't in the global namespace, it is in std:: namespace. I presume likewise with the others (I didn't chase them down).

[mkl]

set(CMAKE_OSX_SYSROOT ...) goes into CMakeLists.txt, not the shell.

[kkaefer]

I ran into this issue as well. It turns out that some pkg-config files (e.g. libcurl) from Homebrew add this path automatically, even if you have Xcode installed. This was fixed in Homebrew 2.2.13. More details in github.com/Homebrew/brew/issues/5068; PR that fixes this is in github.com/Homebrew/brew/pull/7331. TL;DR: Update homebrew

[pahjbo]

Yes it was an old homebrew pkg_config for zlib that was still somehow lying around, that was causing this for me - despite having an up to date homebrew and not currently having a zlib installed anyway

[Tiago Martins Peres]

Hi Niloy Datta! I suggest you to edit this answer removing the question from this answer and include only what answers. If you have a question, then ask separately in the proper way questions should be asked in this community.

[Niloy Datta]

@TiagoMartinsPeres李大仁, removed it. Thanks.

[Hector Esteban]

Thanks man, it worked for me. Do you know a cleaner way to deal with this problem though?

[Niloy Datta]

@VictorSanchez, still trying to figure it out. Will notify once I get it.

[Hector Esteban]

The problem is that when using PCL I have to do the change but other times I just import cmath I have to reverse it

[jbm]

Are there any recommendations on how to fix this? I tried uninstalling both the command line tools and Xcode (11.4.1), but the #include<...> search order is still wrong.

[Ryan H.]

The only thing I can think of is to look in your login scripts such as ~/.bash_profile, ~/.zshrc etc. for things that can affect the search order such as compiler environment variables (in my case it was CPLUS_INCLUDE_PATH) or the order of directories in your PATH.

[hunzter]

Thank you for your details explaination. But sadly no solution seems to work for my machine. I am about to goes for the final option to reinstall Catalina. Damn Apple, why they make things so difficult?

[JerryN]

I followed these directions, from above, to hard code a path to math.h. That worked fine for a while but I suspect that a newer version of Xcode broke this and I was getting compilation errors involving math.h. So don't do this Using #include</Applications/Xcode.app/Contents/Developer/Toolchai‌​ns/XcodeDefault.xcto‌​olchain/usr/include/‌​c++/v1/math.h> instead of <math.h> in /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeD‌​efault.xctoolchain/u‌​sr/include/c++/v1/cm‌​ath!!!

[JerryN]

see my comment above about how hard coding a path to math.h is a bad idea.

[Jake Cobb]

Cause is same as @solodon mentioned. Got this with MacOSX SDK as described here, picked up the SDK usr/include include due to CMake find_package getting e.g. zlib from it. Fix was to put the toolchain usr/include/c++/v1 folder onto the system includes (-isystem to clang, or include_directories(SYSTEM ...) in CMake). I deduced the toolchain directory off the CMAKE_LINKER path rather than hard-code it.

[burlyearly]

Instead of 2, consider changing <cmath> to do #include "./math.h". This avoids having to put the fully-qualified filename in there and still works (for me, at least).

[Vlad]

On my side the problem was fixed by removing directory /Library/Developer/CommandLineTools. I was building Swift for Android on macOS Catalina.

[Cris Luengo]

No matter how I changed the include path order, I couldn't get <cmath> to load the right <math.h>. #include "./math.h" didn't work either. Only including the full path solved the issue for me. I hate that, it's going to give me headaches later on, but it's the only thing that worked for me. libclang must be doing something weird with the search path.

[WeakPointer]

This answer was very helpful for me too. In my case, I had had such an explicit include in my Go CGO_CPPFLAGS environment variable, left over from a project that hasn't been updated to know where the Darwin stdio.h file could be found but llvm wasn't being used explicitly in that one, and I carried that over to a project that was already up to date with building from the latest Darwin but now, needing to have the LLVM c++/v1 files consistent with themselves, that explicit help of where to find Darwin headers was a problem. This was a huge help.

[PacificSky]

This IS the fix. Other suggestions like CMAKE_OSX_SYSROOT or setting CPATH did not help.

[zkoza]

Your method is easy, but dangerous, because it breaks the compiler system (OP may need it for other purposes than Catalina, and will certainly very soon forget about system changes he made). Moreover, it may work only until the next system upgrade. I would not touch the files that come with a compiler, and /usr/local/include/math.h is one of such files.

[chunkyguy]

I had a similar issue due to a file called Math.h in llvm/include/llvm/CodeGen/PBQP/Math.h which gets indirectly referenced from cstdlib.

[Some Guy on the Internet]

I'm using Cmake. It worked for me to add set(CMAKE_OSX_SYSROOT /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.‌​platform/Developer/S‌​DKs/MacOSX10.14.sdk)

[Michael Roswell]

I recently reinstalled command line tools, macos 12.2, ran brew upgrade and still had to do this! Option 2 above totally worked for me today, but why hasn't this been fixed upstream of me?

[Michael Roswell]

Perhaps useful to someone: to edit this file I ran sudo vi /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/incl‌​ude/c++/v1/cmath1, added the new #include line, and closed with esc followed by :x!