Qt 遇到 xcode12 编译报错 ‘string.h‘ file not found
最近升级了 Mac osX 到 10.15.7， 顺便更新了最新的xcode，更新到xcode12， 所有都升级完，也编译了项目，能正常运行，打包也没问题。昨天Qt 代码有修改，顺便从项目git仓库更新项目Qt部分代码，编译Qt代码，出现了很久没有出现的问题：fatal error: 'string.h' file not found， 这个问题之前升级 xcode 或者升级 Mac osX 有出现过类似的问题，按照之前的经验，把编译目录删除重新编译就可以，这次也照样做，结果qmake都过不了，报错了：
Project ERROR: Cannot run target compiler '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++'. Output:
===================
Apple clang version 12.0.0 (clang-1200.0.32.2)
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/include/c++/v1"
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-ios14.0.0 -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 - -mrelocation-model pic -pic-level 2 -mthread-model posix -mframe-pointer=all -fno-strict-return -masm-verbose -munwind-tables -target-sdk-version=14.0 -target-cpu core2 -dwarf-column-info -debugger-tuning=lldb -target-linker-version 609 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk -stdlib=libc++ -internal-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1 -internal-isystem /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/local/include -internal-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/include -internal-externc-isystem /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/include -internal-externc-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include -Wno-reorder-init-list -Wno-implicit-int-float-conversion -Wno-c99-designator -Wno-final-dtor-non-final-class -Wno-extra-semi-stmt -Wno-misleading-indentation -Wno-quoted-include-in-framework-header -Wno-implicit-fallthrough -Wno-enum-enum-conversion -Wno-enum-float-conversion -fdeprecated-macro -fdebug-compilation-dir /Users/derom/Applications/Qt/5.15.1/ios/mkspecs/features -ferror-limit 19 -fmessage-length 0 -stack-protector 1 -fstack-check -mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fobjc-runtime=ios-14.0.0 -fcxx-exceptions -fexceptions -fmax-type-align=16 -fdiagnostics-show-option -o /var/folders/fb/wln8b4nd5sx2vl2bx3gjqng00000gn/T/--211cc3.o -x c++ -
clang -cc1 version 12.0.0 (clang-1200.0.32.2) default target x86_64-apple-darwin19.6.0
ignoring nonexistent directory
11cc3.o -x c++ -
clang -cc1 version 12.0.0 (clang-1200.0.32.2) default target x86_64-apple-darwin19.6.0
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/System/Library/Frameworks (framework directory)
End of search list.
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -no_deduplicate -dynamic -dylib -arch x86_64 -platform_version ios 14.0.0 14.0 -single_module -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk -o /dev/null -v /var/folders/fb/wln8b4nd5sx2vl2bx3gjqng00000gn/T/--211cc3.o -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/lib/darwin/libclang_rt.ios.a
@(#)PROGRAM:ld PROJECT:ld64-609
BUILD 07:59:13 Aug 25 2020
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
Library search paths:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/lib
Framework search paths:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/System/Library/Frameworks/
ld: warning: ignoring file /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/lib/libc++.tbd, missing required architecture x86_64 in file /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/usr/lib/libc++.tbd (4 slices)
ld: building for iOS, but linking in object file built for iOS Simulator, file '/var/folders/fb/wln8b4nd5sx2vl2bx3gjqng00000gn/T/--211cc3.o' for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
===================
Maybe you forgot to setup the environment?这可怎么办，开始还是编译出问题，现在都不能qmake了，彻底绝望，只能重装xcode，重装Qt，疯狂折腾，一上午过去了， 又是百度，又是google，关键是google突然不用，世界突然安静了！只能好好念佛了，心里默念阿弥陀佛！先是重装Qt，还是qmake报错，没办法删除了xcode，准备xcode退回xcode11， xcode11也有7.5G，很大，只能慢慢等，下午也三四点了，又在我的黑苹果上尝试google，突然能访问了（一直 chrome google 助手），如是又google搜索，原来早就有国际友人在用Qt + xcode12，当然是用不了，一样qmake出错，在Qt bug 系统请求帮助，问题严重，Qt大佬是第一时间出现，给也解决方案，修改 mkspecs/features/toolchain.prf 文件
--- a/mkspecs/features/toolchain.prf
+++ b/mkspecs/features/toolchain.prf
@@ -199,7 +199,7 @@ isEmpty($${target_prefix}.INCDIRS) {
cxx_flags += -E -v
output = $$system("$$cmd_prefix $$QMAKE_CXX $$qtMakeExpand($$cxx_flags) -xc++ - 2>&1 $$cmd_suffix", lines, ec)
- !equals(ec, 0): qtCompilerError($$QMAKE_CXX, $$output)
+ !uikit:!equals(ec, 0): qtCompilerError($$QMAKE_CXX, $$output)
rim_qcc {
for (line, output) {加个 “!uikit:”搞定，可以了，具体问题查看Qt bug 系统
qmake cannot run target compiler for iOS Xcode 12（https://bugreports.qt.io/browse/QTBUG-86718）
我只是搬运工，主要是方便国内不能google 同学们，百度确实找不到解决方案!阿弥陀佛！