c++ - 'std::ios_base::ios_base(const std::ios_base&)' is private' 错误，同时为 std::ostram 重载运算符 <<

Question

我有一个看起来像这样的结构:

sturct person
{
    string surname;
    person(string n) : surname(n) {};
}

我需要重载 operator<<对于 std::ostream和 person .我写了这个函数:

std::ostream operator<<(std::ostream & s, person & os)
{
    s << os.surname;
    return s;
}

但我收到此错误:

/usr/include/c++/4.6/bits/ios_base.h|788|error: ‘std::ios_base::ios_base(const std::ios_base&)’ is private|

/usr/include/c++/4.6/bits/basic_ios.h|64|error: within this context

/usr/include/c++/4.6/ostream|57|note: synthesized method ‘std::basic_ios::basic_ios(const std::basic_ios&)’ first required here |

Answer 1

std::ostream 不可复制构造，当您按值返回时，您正在复制构造。虽然return value optimization意味着实际上可能不会进行复制，编译器仍然要求可以进行复制。

此运算符的规范返回值是非常量引用:

std::ostream& operator<<(std::ostream& o, const SomeType& t);