Undefined symbols for architecture i386

Undefined symbols for architecture i386:

"std::string::copy(char *, unsigned long, unsigned long) const", referenced from: ......

出现一大堆莫名其妙的类似于这样的错误，其原因是Deployment Target的问题。只需要在项目设置中的info中将Deployment Target设置为低版本，例如：5.0，再重新编译即可消除该错误。