including C/C++ headers in Xcode 4

Question

I've been using a C++ library without problems on projects built with Xcode 3, but I'm now getting build problems on projects built with Xcode 4.

Drop the library into the Xcode 4 project and it builds fine, but as soon as I #include it, I get a "Lexical or Preprocessor Issue" error, more specifically " 'string' file not found, on line 4 of its main header file.

On closer inspection, the error specifies that 'string' file not found in ~/my project's directory/include/mainheader.h

I've tried the solutions listed here, but none worked.

So it thinks that header file is in my project directory, but it's obviously a C/C++ header… How can I tell Xcode to look for these C/C++ headers?

Are you using `#include "string.h"` or `#include `?There is a difference. — Richard J. Ross III, Jan 16 '12 at 15:26
Shouldn't it be `#include `? I've never heard of just including a file called "string" in c++ — Richard J. Ross III, Jan 16 '12 at 15:29
That's legal, it's a class template (see [here](http://www.cplusplus.com/doc/tutorial/templates/)), Xcode 3 didn't see it as a problem, so this has got something to do with Xcode 4. — Eric, Jan 16 '12 at 15:38
Try Checking your build phases & settings, & make sure that the file is compiling as C++ and not C. — Richard J. Ross III, Jan 16 '12 at 15:39
I checked, that problematic header file has "C++ header" as File Type. — Eric, Jan 16 '12 at 15:45
@Eric: but what about all the files it is included in? They must all be C++ or Objective-C++ — JeremyP, Jan 16 '12 at 17:00
I do that `#include` in my main header file, which is a C header. I'm still getting that problem when I set its file type as "C++ header". — Eric, Jan 16 '12 at 17:57

Eric · Accepted Answer · 2012-01-17T21:20:28.027

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The problematic #include was at the top of my ViewController.mm, which I had already turned into Objective-C++ by giving it .mm as its extension. But ViewController.mm gets eventually imported by AppDelegate.m, which is Objective-C by default – and I had forgotten to make it Objective-C++, hence the problem.

So renaming AppDelegate.m to AppDelegate.mm solved the problem.

edited Jan 17 '12 at 21:20

answered Jan 17 '12 at 20:58

Eric

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score 0 · Answer 2 · answered Jan 16 '12 at 18:26

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I think #include is a c++ class template..so you need to used using namespace std in your header file and also rename your source file .m format to .mm format.

it works for me :) try this...

answered Jan 16 '12 at 18:26

Saif

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I'm not familiar with xCode and OSX/iOS development, but this statement - *#include is a c++ class template* - is definitely not correct. – Andrejs Cainikovs Jan 16 '12 at 18:37
The C++ Standard Template Library (STL) contains a string class that is used in several computer science classes. Check this :: http://www.bgsu.edu/departments/compsci/docs/string.html http://www.cplusplus.com/reference/string/string/string/ http://www.cplusplus.com/reference/string/string/ – Saif Jan 16 '12 at 18:39
Thanks, but none of your links shows the explanation. This page has it at the very end: http://www.cplusplus.com/doc/tutorial/templates/ – Andrejs Cainikovs Jan 16 '12 at 18:40
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Putting `using namespace ANYTHING;` in a header is not a good idea. There is no point having namespaces in that case. – dreamlax Jan 16 '12 at 19:06
@saif Your solution (renaming the source file) is probably correct, but the answer is a bit confusing. `std::string` is not a template, but it is a class. I think you might mean "class declaration". `#include` is a way to read other files, regardless of their contents. – Per Johansson Jan 17 '12 at 08:04

including C/C++ headers in Xcode 4

2 Answers2