[英]understanding the operator<<() from std::cout
I have written this little code for one of my student coworker, in order to illustrate overloading in c++:我为我的一位学生同事编写了这个小代码,以说明 c++ 中的重载:
#include <iostream>
int main() {
std::cout << "Hello World!";
std::cout.operator<<("Hello World!");
return 0;
}
I thought naively I will have two times "Hello World.".我天真地以为我会有两次“Hello World”。 But the second line send me an adress?
但是第二行给我一个地址? I don't understand why ?
我不明白为什么?
According to cppreference (emphasis mine):根据cppreference (强调我的):
Character and character string arguments (eg, of type char or const char*) are handled by the non-member overloads of operator<< .
字符和字符串 arguments(例如,char 或 const char* 类型)由operator<< 的非成员重载处理。 [...] Attempting to output a character string using the member function call syntax will call overload (7) and print the pointer value instead.
[...] 使用成员 function 调用语法尝试 output 字符串将调用重载(7)并打印指针值。
So in your case, calling the member operator<<
will indeed print the pointer value, since std::cout
does not have an overload for const char*
.因此,在您的情况下,调用成员
operator<<
确实会打印指针值,因为std::cout
没有const char*
的重载。
Instead you can call the free function operator<<
like this:相反,您可以像这样调用免费的 function
operator<<
:
#include <iostream>
int main() {
std::cout << "Hello World!"; //prints the string
std::cout.operator<<("Hello World!"); //prints the pointer value
operator<<(std::cout, "Hello World!"); //prints the string
return 0;
}
If an operator is a member function then如果操作员是成员 function 则
object operator other_operand
is equivalent to相当于
object.operator(other_operand)
However, if the operator is not a member then it is rather但是,如果操作员不是成员,那么它是
operator(object,other_operand)
Here you can find the list of overloads of <<
that are members https://en.cppreference.com/w/cpp/io/basic_ostream/operator_ltlt在这里您可以找到成员
<<
://en.cppreference.com/w/cpp/io/basic_ostream/operator_ltlt的重载列表
And here the list of overloads that are non members https://en.cppreference.com/w/cpp/io/basic_ostream/operator_ltlt2这里是非成员的重载列表https://en.cppreference.com/w/cpp/io/basic_ostream/operator_ltlt2
Note that the operator<<
for char*
is not a member!请注意,
char*
的operator<<
不是成员! But there is a member operator<<
for void*
that can print the value of a pointer of any type.但是有一个成员
operator<<
for void*
可以打印任何类型的指针的值。
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