Why does ostream::operator<< allow ostringstream arg?

Asked Jul 27 '16 at 15:42

Active Jul 27 '16 at 15:46

Viewed 29 times

This produces garbage:

#include <iostream>
#include <sstream>
main()
{
    std::ostringstream s1;
    s1 << "s" << 1;
    std::cout << s1 << std::endl;
}

This produces garbage. I realize the fix is to use s1.str(). I'm wondering why ostream::operator<< can take the ostringstream arg if it "doesn't work properly".

edited Jul 27 '16 at 15:46

asked Jul 27 '16 at 15:42

John H.

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this [doesn't compile for me on either gcc or clang](http://coliru.stacked-crooked.com/a/d213d94b7b5638a2). What compiler and version are you using? – jaggedSpire Jul 27 '16 at 15:44
Doesn't compile with [Visual Studio 2015 either](http://rextester.com/WZPW65979) – PaulMcKenzie Jul 27 '16 at 15:46
@jaggedSpire Probably a pre-C++11 one. – Sebastian Redl Jul 27 '16 at 15:46
@SebastianRedl [looks like you're right](http://coliru.stacked-crooked.com/a/63d66f63a98d11cf) – jaggedSpire Jul 27 '16 at 15:48
Where is your return type for `main`? – Lightness Races in Orbit Jul 27 '16 at 15:56
@jaggedSpire g++ (GCC) 4.8.3, with -std=c++11 -- and I gather (per the 'duplicate' answer) that this is a known issue in g++. – John H. Jul 27 '16 at 16:56
@JohnH. well the explanation dupe-linked is the probable one. It seems any version of gcc after 5.0 changes the behavior to the expected compiler error, though. You might want to upgrade your compiler if you can--gcc head is presently at 7.0, and 6.1's pretty common. – jaggedSpire Jul 27 '16 at 17:02
@jaggedSpire Corporate is moving to 5.2 Any Day Now... Thanks much for all you's help. – John H. Jul 27 '16 at 19:01

Why does ostream::operator<< allow ostringstream arg?

0 Answers0