Question

I am developing an application that needs to work on Linux, Windows and Mac OS X. To that purpose, I am using C++ with Qt.

For many reasons, on Mac OS X, I need to use CoreFoundation functions (such as CFBundleCopyBundleURL) that creates core objects that need to be released with CFRelease. But doing so generate a lots of these warnings:

*** __NSAutoreleaseNoPool(): Object 0x224f7e0 of class NSURL autoreleased with no pool in place - just leaking

All the code I’ve seen concerning these autorelease pools is written in Objective-C. Does anybody know how to create/use autorelease pools in C or C++?

Answer 1

id is a C declaration. You can simply add scope based autorelease pools to your cpp program like so:

autorelease_pool.hpp

class t_autorelease_pool {
public:
    t_autorelease_pool();
    ~t_autorelease_pool();
private:
    id d_pool; // << you may opt to preprocess this out on other platforms.
private:
    t_autorelease_pool(const t_autorelease_pool&);
    t_autorelease_pool& operator=(const t_autorelease_pool&);
};

autorelease_pool.mm

t_autorelease_pool::t_autorelease_pool() : d_pool([NSAutoreleasePool new]) {}
t_autorelease_pool::~t_autorelease_pool() { [this->d_pool drain]; }

In a cpp program:

void UpdateUI() {
    t_autorelease_pool pool;
    // your/their autoreleasing code here
}

---

An alternative (which can be very easy to use incorrectly) is to use the ObjC runtime directly – which would look like the following C program:

#include <objc/runtime.h>
#include <objc/message.h>
...
id pool = objc_msgSend(objc_getClass("NSAutoreleasePool"), sel_getUid("new")); 
/* do stuff */
objc_msgSend(pool, sel_getUid("drain"));