关于C ++中的std：cout

Question

Is there an error in this code:

#include <iostream>
using namespace std;

int main()
{
    std:cout << "hello" "\n";
}

GCC detects no error but std:cout does not seem standard.

Answer 1

There's no error. I could rewrite your code to make it clearer:

#include <iostream>
using namespace std;

int main()
{
std:
    cout << "hello" "\n";
}

You created a label named std . cout is used unqualified, which is okay since you have the using-directive for std above it. And you can concatenate string literals by writing them next to each other as you did. This is perfectly well-formed code that prints "hello" followed by a newline.

Answer 2

You're defining a label std and then you're calling cout . This is legal because you have using namespace std;

Answer 3

The code has an issue. while trying to instruct the compiler to use the namespace std, we are trying to call the function cout which is defined in the scope of std.

thus the correct use of the scope resolution operator is

    'std::cout '

and not

    std:cout.

And others have pointed out by writing

    std:

what you do is create a label.