C++ 中的 toString 重写

发布于 2024-10-20 03:33:02 字数 408 浏览 6 评论 0原文

在 Java 中，当一个类重写 .toString() 并且您执行 System.out.println() 时，它将使用它。

class MyObj {
    public String toString() { return "Hi"; }
}
...
x = new MyObj();
System.out.println(x); // prints Hi

我如何在 C++ 中实现这一点，以便：

Object x = new Object();
std::cout << *x << endl;

输出我为 Object 选择的一些有意义的字符串表示形式？

原文

In Java, when a class overrides .toString() and you do System.out.println() it will use that.

class MyObj {
    public String toString() { return "Hi"; }
}
...
x = new MyObj();
System.out.println(x); // prints Hi

How can I accomplish that in C++, so that:

Object x = new Object();
std::cout << *x << endl;

Will output some meaningful string representation I chose for Object?

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中二柚 2024-10-27 03:33:02

std::ostream & operator<<(std::ostream & Str, Object const & v) { 
  // print something from v to str, e.g: Str << v.getX();
  return Str;
}

如果将其写入头文件中，请记住将该函数标记为内联： inline std::ostream &运算符<<(...（请参阅 C++ 超级常见问题解答为什么。）

std::ostream & operator<<(std::ostream & Str, Object const & v) { 
  // print something from v to str, e.g: Str << v.getX();
  return Str;
}

If you write this in a header file, remember to mark the function inline: inline std::ostream & operator<<(... (See the C++ Super-FAQ for why.)

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樱花坊 2024-10-27 03:33:02

作为埃里克解决方案的替代方案，您可以覆盖字符串转换运算符。

class MyObj {
public:
    operator std::string() const { return "Hi"; }
}

通过这种方法，您可以在需要字符串输出的任何地方使用对象。您不限于流。

然而，这种类型的转换运算符可能会导致无意的转换和难以追踪的错误。我建议仅将其与具有文本语义的类一起使用，例如 Path、UserName 和 SerialCode。

Alternative to Erik's solution you can override the string conversion operator.

class MyObj {
public:
    operator std::string() const { return "Hi"; }
}

With this approach, you can use your objects wherever a string output is needed. You are not restricted to streams.

However this type of conversion operators may lead to unintentional conversions and hard-to-trace bugs. I recommend using this with only classes that have text semantics, such as a Path, a UserName and a SerialCode.

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饮惑 2024-10-27 03:33:02

 class MyClass {
    friend std::ostream & operator<<(std::ostream & _stream, MyClass const & mc) {
        _stream << mc.m_sample_ivar << ' ' << mc.m_sample_fvar << std::endl;
    }

    int m_sample_ivar;
    float m_sample_fvar;
 };

 class MyClass {
    friend std::ostream & operator<<(std::ostream & _stream, MyClass const & mc) {
        _stream << mc.m_sample_ivar << ' ' << mc.m_sample_fvar << std::endl;
    }

    int m_sample_ivar;
    float m_sample_fvar;
 };

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So尛奶瓶 2024-10-27 03:33:02

虽然运算符重写是一个很好的解决方案，但我对像下面这样的更简单的解决方案感到满意（这似乎也更适合 Java）：

char* MyClass::toString() {
    char* s = new char[MAX_STR_LEN];
    sprintf_s(s, MAX_STR_LEN, 
             "Value of var1=%d \nValue of var2=%d\n",
              var1, var2);
    return s;
}

Though operator overriding is a nice solution, I'm comfortable with something simpler like the following, (which also seems more likely to Java) :

char* MyClass::toString() {
    char* s = new char[MAX_STR_LEN];
    sprintf_s(s, MAX_STR_LEN, 
             "Value of var1=%d \nValue of var2=%d\n",
              var1, var2);
    return s;
}

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