CocoaPods：链接到libPods.a中定义的C ++符号 [英] CocoaPods: Linking with C++ symbols defined in libPods.a

问题描述

我最近开始工作在一个podSpec文件，将levelDB集成到我的项目。
（ https://github.com/但是，当我从.mm文件中引用任何C ++符号时，会出现这样的情况：

在主目标，我得到一个链接器错误，像这样：

 架构x86_64的未定义符号：
leveldb： ：DB :: Open（leveldb :: Options const& std :: __ 1 :: basic_string< char，std :: __ 1 :: char_traits< char> ;, std :: __ 1 :: allocator< char>> const& leveldb :: DB **），引用自：
  -  IHLevelDBContext.o中的[IHLevelDBContext initWithPath：] 
  

$ b b

这是编译器调用的样子。

  /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault .xctoolchain / usr / bin / clang ++ -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk -L / Users / ilja / Library / Developer / Xcode / DerivedData / LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao / Build / Products / Debug -F / Users / ilja / Library / Developer / Xcode / DerivedData / LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao / Build / Products / Debug-filelist / Users / DerivedData / LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao / Build / Intermediates / LevelDBTest2.build / Debug / LevelDBTest2.build / Objects-normal / x86_64 / LevelDBTest2.LinkFileList -mmacosx-version-min = 10.7 -ObjC -fobjc-arc -fobjc-link- stdlib = libc ++ -framework Cocoa -lPods -o /Users/ilja/Library/Developer/Xcode/DerivedData/LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao/Build/Products/Debug/LevelDBTest2.app/Contents/MacOS/LevelDBTest2 
  
 
 
 
根据我的理解，缺少的:: Open调用包含在libPods.a中
  nm libPods.a | grep的打开
 
ü__ZN7leveldb2DB4OpenERKNS_7OptionsERKSsPPS0_ 
 000000000005e5b1。S L ___ FUNC __._ ZN7leveldb6DBImpl24OpenCompactionOutputFileEPNS0_15CompactionStateE 
 00000000000099d0牛逼__ZN7leveldb2DB4OpenERKNS_7OptionsERKSsPPS0_ 
 0000000000060ba0小号__ZN7leveldb2DB4OpenERKNS_7OptionsERKSsPPS0_.eh 
  
看来我可以通过将主程序的编译器设置从Apple LLVM 4.2更改为LLVM GCC 4.2来解决链接器错误，阻塞了Objective-C 2.0的特性，像这样：
 预期'strong'前的属性属性
  Ilja 
解决方案
您还可以在podspec文件中设置C ++配置设置：
  s.library ='c ++'
 s.xcconfig = {
'CLANG_CXX_LANGUAGE_STANDARD'=> 'c ++ 11'，
'CLANG_CXX_LIBRARY'=> 'libc ++'
} 
  
 
 
这些设置选择为C ++ 2011编译并添加libc ++标准库。
 
I recently started working on a podSpec file that integrates levelDB into my projects.
(https://github.com/iljaiwas/Podspecs/blob/master/LevelDBPodSpec/0.0.1/leveldb.podspec)

However, when I reference any C++ symbol from a .mm file in the main target, I get a linker error like this:
Undefined symbols for architecture x86_64:
 "leveldb::DB::Open(leveldb::Options const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, leveldb::DB**)", referenced  from:
  -[IHLevelDBContext initWithPath:] in IHLevelDBContext.o
This is what the compiler invocation looks like
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk -L/Users/ilja/Library/Developer/Xcode/DerivedData/LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao/Build/Products/Debug -F/Users/ilja/Library/Developer/Xcode/DerivedData/LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao/Build/Products/Debug -filelist /Users/ilja/Library/Developer/Xcode/DerivedData/LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao/Build/Intermediates/LevelDBTest2.build/Debug/LevelDBTest2.build/Objects-normal/x86_64/LevelDBTest2.LinkFileList -mmacosx-version-min=10.7 -ObjC -fobjc-arc -fobjc-link-runtime -stdlib=libc++ -framework Cocoa -lPods -o /Users/ilja/Library/Developer/Xcode/DerivedData/LevelDBTest2-aiflqgbevhxzfxbrsdamteybrbao/Build/Products/Debug/LevelDBTest2.app/Contents/MacOS/LevelDBTest2 
From my understanding, the missing ::Open call is included in libPods.a
nm libPods.a | grep "Open"

             U __ZN7leveldb2DB4OpenERKNS_7OptionsERKSsPPS0_
000000000005e5b1 s L___func__._ZN7leveldb6DBImpl24OpenCompactionOutputFileEPNS0_15CompactionStateE
00000000000099d0 T __ZN7leveldb2DB4OpenERKNS_7OptionsERKSsPPS0_
0000000000060ba0 S __ZN7leveldb2DB4OpenERKNS_7OptionsERKSsPPS0_.eh
It seems I can get around the linker errors by changing the "Compiler" setting for the main app from Apple LLVM 4.2 to LLVM GCC 4.2, but this compiler chokes on Objective-C 2.0 features, like this: 
expected a property attribute before 'strong' 
Thanks for any pointers on what I might be doing wrong,
Ilja
解决方案
You can also set the C++ config settings in the podspec file:
  s.library = 'c++'
  s.xcconfig = {
       'CLANG_CXX_LANGUAGE_STANDARD' => 'c++11',
       'CLANG_CXX_LIBRARY' => 'libc++'
  }
Those settings selects to compile for C++ 2011 and adds the libc++ standard library.

                        
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