Printing the smiley-with-beard lambda expression

Question

I tried printing the smiley-with-beard lambda expression

#include <iostream>

int main() {
    std::cout << <:]{%>; // smile!
    return 0;
}

but it printed

instead. How?

Probably it triggers an implicit conversion to a non-null pointer to function and is printed as a boolean — Piotr Skotnicki, Oct 06 '15 at 18:42

score 5 · Accepted Answer · edited May 23 '17 at 12:15

5

As explained in the answers to the question you've linked to,

<:]{%>

is equivalent to

[]{}

A lambda expression that doesn't capture anything is implicitly convertible to a function pointer. In this case, the signature of this function pointer is void(*)().

Now, the function pointer is implicitly convertible to a boolean value which is always true, hence the output prints 1.

edited May 23 '17 at 12:15

Community

1
1

answered Oct 06 '15 at 18:47

Praetorian

103,386
18
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score 2 · Answer 2 · answered Oct 06 '15 at 18:42

2

You forgot to put " around <:]{%>.

You should have :

std::cout << "<:]{%>";

answered Oct 06 '15 at 18:42

N. Hereman

33
6

Printing the smiley-with-beard lambda expression

2 Answers2