c++ - 链接器命令在macOS上失败，退出代码为1(使用-v查看调用)

Question

我正在基于示例练习一个简单的C++代码

class Tset{
    public:
        Tset();
        Tset operator+( const Tset& a);

};

Tset Tset::operator+(const Tset& a){
    Tset t;
    return t;
}

但是当我用g++编译这段代码时
发生这个错误

Mac Desktop % g++ hw2.cpp
Undefined symbols for architecture x86_64:
  "Tset::Tset()", referenced from:
      Tset::operator+(Tset const&) in hw2-43d108.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

谁能告诉我怎么了？

这是我的g++版本:

Mac Desktop % g++ -v     
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
Apple clang version 11.0.0 (clang-1100.0.33.12)
Target: x86_64-apple-darwin19.0.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Answer 1

问题是您尚未提供构造函数的定义。

此函数隐式调用构造函数Tset::Tset():

Tset Tset::operator+(const Tset& a){
    Tset t;    // Requires definition of constructor.
    return t;
}

但是在您的类中，您没有定义构造函数:

class Tset {
public:
    Tset();            // No definition.  :-(
    Tset operator+(const Tset& a);
};

您可以通过提供构造函数的定义或默认构造函数来解决此问题:

class Tset {
public:
    Tset() = default;
    Tset operator+( const Tset& a);
};