Compile errors with #include <string> in Cocoa App

Question

I am trying to compile a Cocoa app in xcode 4.0 and I'm getting this error...

fatal error: 'string' file not found

...when trying to compile to .pch file on this line:

#include <string>

I have another xcode project that does the same thing, but does not get the error. I have scoured the build settings for some different, but I can't find one. The only difference is that the project that compiles OK was started as a command line project, not a Cocoa project, but the build setting are the same.

The target OS is Mac OS X 10.6

The error happens when compiling the precompiled header and doesn't get to any of the other files. The only framework that the compiling version has is Foundation.framework and the non-compiling one has it as well.

Why is it not finding in one project and not the other? Any advice?

Answer 1

What is the extension of your source files? If it is ".m", try to change it to obj-cpp ".mm", so that Xcode will deduce correct language. Or just put c++-specific headers inside "#ifdef __cplusplus" block

Update

The guard must exist for each language compiled in the project because this specific include is in the pch. IOW, if it were all c++ and/or objc++ there would be no error. Evidently, there is at least one file that does not recognize C++ (e.g. C or ObjC sources are also compiled in the target). Therefore, you simply guard it like so:

// MONPrefix.pch

#ifdef __cplusplus
#include <string>
#endif

// same for objc, so your C and C++ sources compile with no error:
#ifdef __OBJC__
#include <Foundation/Foundation.h>
#endif