在开发iOS程序的过程中，通常在导入第三方的类库（.a/.o）文件会报出一系列的错误：
Undefined symbols for architecture i386:
"std::string::c_str() const", referenced from:
MP4Chunk::putTag(std::string) in libHKSUMEyeSDK.a(MP4Chunk.o)
"std::string::empty() const", referenced from:
MP4Chunk::putTag(std::string) in libHKSUMEyeSDK.a(MP4Chunk.o)
"std::allocator<char>::allocator()", referenced from:
MP4Chunk::writeFtypTag() in libHKSUMEyeSDK.a(MP4Chunk.o)
MP4Chunk::writeFreeTag() in libHKSUMEyeSDK.a(MP4Chunk.o)
MP4Chunk::writeMdatTag() in libHKSUMEyeSDK.a(MP4Chunk.o)
MP4Chunk::writeMoovTag() in libHKSUMEyeSDK.a(MP4Chunk.o)
MP4Chunk::writeMvhdTag() in libHKSUMEyeSDK.a(MP4Chunk.o)
MP4Chunk::WriteIODS() in libHKSUMEyeSDK.a(MP4Chunk.o)
MP4Chunk::writeTrakTag() in libHKSUMEyeSDK.a(MP4Chunk.o)
看似缺少了某个类库文件，但多次检查之后发现，没缺少啥引用的，甚至跟原来的Demo一个都不差，这是怎么回事？
由于第三方类库多数是用C++或者C编写的，在引用过程中，还需要告诉编译器可能会出现的语言种类，以便使用对应的解释器进行解析。
OK，那么我们只需要在XCode环境中检查以下几个配置项是否与下面一致即可：
TARGETS->Build Settings,搜索
1.Other Linker Flags:-ObjC
2.C++ Language Dialect:Compiler Default
3.C++ Standard Library:Compiler Default
4.Compile Sources As:Objective-C++或者设置为According to File Type,然后将引用到C++类库的文件后缀改为“.mm”。
iOS开发引入第三方类库的问题,布布扣,bubuko.com
原文：http://www.cnblogs.com/jaenson/p/3892384.html