std::ostream class 中的对象是 "not accessible through a pointer or object"

Question

我在 class 中使用了几个函数，这些函数通过函数接口传递给一个 ostream，后者又可用于输出错误消息。我曾希望能够将所有 ostream 绑定到一个对象，然后在必要时将其重定向到一个文件。

我的代码的相关部分如下所示：

#include <iostream>

class Example
{
    public:
    Example(){} //<--Error: "std::basic_ostream<_CharT, _Traits>::basic_ostream() [with _CharT=char, _Traits=std::char_traits<char>]" (declared at line 390 of "/usr/include/c++/9/ostream") is inaccessible C/C++(330)

    void DoSomething()
    {
        FunctionWithOstream(out);
    }

    private:
    std::ostream out; //in my case, the ostream is currently not needed for the time being.

    void FunctionWithOstream(std::ostream& out)
    {
        out << "Something";
    }
};

在构造函数（或程序中的所有构造函数）的第一个大括号处，我收到以下错误消息：

protected function "std::basic_ostream<_CharT, _Traits>::basic_ostream() [with _CharT=char, _Traits=std::char_traits]" (declared at line 390 of "/usr/include/c++/9/ostream") is not accessible through a "std::basic_ostream<char, std::char_traits>" pointer or objectC/C++(410)

或者我在此处粘贴的简短示例代码：

"std::basic_ostream<_CharT, _Traits>::basic_ostream() [with _CharT=char, _Traits=std::char_traits]" (declared at line 390 of "/usr/include/c++/9/ostream") is inaccessibleC/C++(330)

我希望问题足够清楚，提前感谢您的宝贵时间。

问候蒂尔曼

Answer 1

好的，我找到了解决方案：

#include <iostream>
#include <sstream>

class Example
{
    public:
    Example(){} //<--Error: "std::basic_ostream<_CharT, _Traits>::basic_ostream() [with _CharT=char, _Traits=std::char_traits<char>]" (declared at line 390 of "/usr/include/c++/9/ostream") is inaccessible C/C++(330)

    void DoSomething()
    {
        FunctionWithOstream(outStream);
    }

    private:
    std::ostringstream outStream; //std::ostringstream instead of std::ostream is working fine.

    void FunctionWithOstream(std::ostream& out)
    {
        out << "Something";
    }
};

而不是 std::ostream std::ostringstream 可用于接收函数流。

Answer 2

std::ostream 不是默认构造的，您可能需要 reference/pointer 代替：

class Example
{
public:
    Example(std::ostream& out = std::cout) : out(out) {}

    void DoSomething() { FunctionWithOstream(out); }

private:
    std::ostream& out;

    void FunctionWithOstream(std::ostream& os) { os << "Something"; }
};

std::ostream class 中的对象是 "not accessible through a pointer or object"

std::ostream object in class is "not accessible through a pointer or object"

c++

c++11

iostream

ostream