我使用brew install llvm安装LLVM 8，并且想使用命令行工具。我已经按照Homebrew的建议设置了clang可执行文件的路径（在/usr/local/opt/llvm/bin中），并按照他们的建议设置了LDFLAGS和CPPFLAGS。当我编译一个简单的程序时，我会得到
x.c:1:10: fatal error: 'stdio.h' file not found
#include <stdio.h>
^~~~~~~~~
1 error generated.
阅读xcrun和xcode-select的文档，我认为应该有一种简单的方法来选择我的LLVM工具链，但我不知道。我尝试更改TOOLCHAINS和SDKROOT失败了。
对于Homebrew的llvm-8，clang -v -c x.c的输出
clang version 8.0.0 (tags/RELEASE_800/final)
Target: x86_64-apple-darwin18.5.0
Thread model: posix
InstalledDir: /usr/local/opt/llvm/bin
"/usr/local/Cellar/llvm/8.0.0/bin/clang-8" -cc1 -triple x86_64-apple-macosx10.14.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name x.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu penryn -dwarf-column-info -debugger-tuning=lldb -ggnu-pubnames -target-linker-version 409.12 -v -coverage-notes-file /tmp/x.gcno -resource-dir /usr/local/Cellar/llvm/8.0.0/lib/clang/8.0.0 -fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=macosx-10.14.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o x.o -x c x.c
clang -cc1 version 8.0.0 based upon LLVM 8.0.0 default target x86_64-apple-darwin18.5.0
ignoring nonexistent directory "/usr/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/usr/local/Cellar/llvm/8.0.0/lib/clang/8.0.0/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
x.c:1:10: fatal error: 'stdio.h' file not found
#include <stdio.h>
^~~~~~~~~
1 error generated.
系统clang的输出：
Apple LLVM version 10.0.1 (clang-1001.0.46.3)
Target: x86_64-apple-darwin18.5.0
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 x86_64-apple-macosx10.14.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name x.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables -target-sdk-version=10.14 -target-cpu penryn -dwarf-column-info -debugger-tuning=lldb -target-linker-version 450.3 -v -coverage-notes-file /tmp/x.gcno -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk -I/usr/local/include -Wno-atomic-implicit-seq-cst -Wno-framework-include-private-from-public -Wno-atimport-in-framework-header -Wno-quoted-include-in-framework-header -fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=macosx-10.14.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o x.o -x c x.c
clang -cc1 version 10.0.1 (clang-1001.0.46.3) default target x86_64-apple-darwin18.5.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/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
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks (framework directory)
End of search list.
答案 0 :(得分：0)
您应该将丢失的标头/库安装为noted in this question。
或者，您应该将clang指向另一个“ sysroot”，例如：
clang -isysroot `xcrun --show-sdk-path` hello.c