c – 为什么我在这个简单的代码中得到“ld：warning：在_main中

参见英文答案 > xcode with boost : linker(Id) Warning about visibility settings????????????????????????????????????6个
这是我的Clang编译器中非常奇怪的行为.我使用Xcode(OS X),所有都是最新的.为什么我会在这个简单的代码中收到此警告？如果我删除这两行警告隐藏.

ld: warning: direct access in _main to global weak symbol
std::__1::char_traits::eq(char,char) means the weak symbol
cannot be overridden at runtime. This was likely caused by different
translation units being compiled with different visibility settings.

int main( int argc,char* argv[] ) {
    std::string file = "test";
    size_t pos = file.find( "a" );
    return 0;
}