Can't std::ostream output a const char array?
The fact that #include <iostream>
was likely missing was deduced using the Sherlock Holmes approach to debugging: "when you have eliminated the impossible, whatever remains, however improbable, must be the truth".
Clearly. std::ostream
should've have had no problems accepting a const char *
overload.
Therefore, an overload resolution complaint must mean that <iostream>
wasn't included. Most C++ library classes are forward-declared all over the place. Including some random header file is likely to get you a forward declaration of std::ostream
, as a free bonus. So the compiler will not complain about this class not being defined.
But unless <iostream>
is included, the compiler will not know about all the overloads that are defined there. That's it.
J. Allan
Quick Facts: (No particular order.) Christian. Male. United States citizen. Programmer. (PHP, Python, C, C++, js, HTML, CSS) Volunteer designer and maintainer of Evangelism Mission's website. Linux Mint user. ESTJ, apparently. Reader (but only when in possession of a good book). Guitar player/songwriter/singer. (It's important to have a little balance.) Favorite Answers: Keep aspect ratio on absolutely positioned element. ~ Algebra IS useful. Can't push more than 4 buttons in canvas game. ~ Sometimes coding problems are hardware problems...
Updated on June 04, 2022Comments
-
J. Allan almost 2 years
For the fun and experience of it, I'm
modifying andexploring the source code for Blobby Volley 2 1.0 (Linux).Well... I would be modifying the source code, but I can't even get the program to compile. (Sad, isn't it?)
Here's the code that causes the error:
std::ostream& operator<<(std::ostream& stream, const ServerInfo& val) { return stream << val.name << " (" << val.hostname << ":" << val.port << ")"; }
Trying to compile this with g++ 5.4.0 gives the following (simplified output--the original output is ~443 lines) error message:
error: no match for ‘operator<<’ (operand types are ‘std::ostream {aka std::basic_ostream}’ and ‘const char [32]’)
return stream << val.name << " (" << val.hostname << ":" << val.port << ")";
I simplified the code to this:
std::ostream& operator<<(std::ostream& stream, const ServerInfo& val) { stream << "hello"; //can't get simpler than this, right? return stream; }
and got
error: no match for ‘operator<<’ (operand types are ‘std::ostream {aka std::basic_ostream}’ and ‘const char [6]’)
stream << "hello";
The code that calls it looks like this:
std::cout << "duplicate server entry\n"; std::cout << info << "\n"; //it's called here
The thing I find most surprising is that we all know that
std::cout
and its ilk can handlechar
arrays.For instance,
#include <iostream> #include <string> int main () { const char a[6] = "hello"; std::cout << a << std::endl; //No problem here! return 0; }
works without a hitch.
Oh, one more thing.
If I include
<string>
, this works:std::ostream& operator<<(std::ostream& stream, const ServerInfo& val) { stream << std::string("hello"); return stream; }
Does anyone know what I'm missing?
PS: Here's a pastebin of the errors.
PPS: Here's the headers that were requested:
/* header include */ #include "NetworkMessage.h" /* includes */ #include <cstring> #include "UserConfig.h" #include "SpeedController.h"
PPS: If you are wondering why I didn't get an error about
std::ostream
not being defined, check the 3rd paragraph of Sam's answer. -
vilpan almost 7 years
#include <ostream>
(which declares theconst char*
overload - 27.7.3.1) would suffice instead ofiostream
(which includesostream
- 27.4.1).