Question

有3个文件：

MyClass.h：

#ifndef LABEL
#define LABEL

class MyClass {
public:
    std::string toStr() const;
    friend std::ostream& operator << (std::ostream&, const MyClass&);
};

#endif

MyClass.cpp：

#include <string>
#include "MyClass.h"

std::string MyClass::toStr() const {
    std::string str = "some text";
    return str;
}

std::ostream& operator << (std::ostream& os, const MyClass& obj) {
    return os << obj.toStr();
}

main.cpp：

#include <iostream>
#include "MyClass.h"

int main() {
    MyClass a;
    std::cout << a << std::endl;
    return 0;
}

使用GCC 5.1（g++-5 main.cpp BigInteger.cpp -std=c++11）编译它们不会导致错误，但在使用clang（clang++ main.cpp BigInteger.cpp -std=c++11）进行编译时会产生以下错误：

Undefined symbols for architecture x86_64:
  "std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::operator<<<char, std::__1::char_traits<char>, std::__1::allocator<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)", referenced from:
      operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, MyClass const&) in BigInteger-a5ec56.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

出了什么问题？

P.S。 OS X Yosemite。铿锵版：

Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.3.0
Thread model: posix

为什么clang导致错误？

0 个答案: