C++ 中的 toString 覆盖
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原文地址: http://stackoverflow.com/questions/5171739/
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toString override in C++
提问by Aillyn
In Java, when a class overrides .toString()and you do System.out.println()it will use that.
在 Java 中，当一个类覆盖.toString()并且您执行System.out.println()它时，它将使用它。
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:
我怎样才能在 C++ 中实现这一点，以便：
Object x = new Object();
std::cout << *x << endl;
Will output some meaningful string representation I chose for Object?
会输出一些我选择的有意义的字符串表示Object吗？
回答by Erik
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.)
如果你把它写在头文件中，记得把函数标记为内联：（inline std::ostream & operator<<(...请参阅 C++ Super-FAQ了解为什么。）
回答by Tugrul Ates
Alternative to Erik's solution you can override the string conversion operator.
作为 Erik 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"; }
}
With this approach, you can use your objects wherever a string output is needed. You are not restricted to streams.
通过这种方法，您可以在需要字符串输出的任何地方使用您的对象。您不仅限于流。
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 UserNameand a SerialCode.
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。我建议仅将它用于具有文本语义的类，例如 a Path、 aUserName和 a SerialCode。
回答by Parsa Jamshidi
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;
};
回答by Touhid
Though operator overriding is a nice solution, I'm comfortable with something simpler like the following, (which also seems more likely to Java) :
尽管运算符覆盖是一个不错的解决方案，但我对以下更简单的东西感到满意（这似乎也更可能适用于 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;
}
