Is this output valid or a compiler bug?

Question

#include <iostream>
#include <string>

int main(int argc, char *argv[])
{
    std::string s = {123};
    std::cout << s << std::endl;
}

Why does this program print { as an output? Is it a bug in the underlying lexer that it only prints the preceeding {?

I compiled this with g++ 4.8.1 (with no errors or warnings). MSVC doesn't compile this complaining that string isn't an aggregate type.

Similar: http://stackoverflow.com/questions/15736282/what-is-this-smiley-with-beard-expression — legends2k, Jun 28 '13 at 22:55

Andy Prowl · Accepted Answer · 2013-06-28T22:44:15.017

You are list-initializing a string with an array of characters. 123 is the ASCII code of {. There is no compiler bug.

The constructor you are invoking is the initalizer-list constructor of std::string (see here for a reference), as specified by paragraph 21.4.2/15 of the C++11 Standard:

basic_string(std::initializer_list<CharT> init, 
             const Allocator& alloc = Allocator());
Effects: Same as basic_string(il.begin(), il.end(), a).

MSVC does not support list-initialization, which is why you are getting the message complaining about the fact that string is not an aggregate.

Is this output valid or a compiler bug?

1 Answers1