Using NSProcessInfo from C++ - c++

Question

Is it possible to use [[NSProcessInfo processInfo] operatingSystemVersion] from C++ or C and how do I do that?

Answer 1

In XCode and Objective-C, files with extension .mm are treated as "mixed" in the sense that one single file can contain C++/C notion as well as Objective-C code, and that even C++/C function implementations can access Objective-C classes and send messages to them.
Such a .mm-files can then provide a trampoline function, i.e. a C-style function that is exposed and can then be used in pure C++/C-files (extension .cpp, where Objective-C code must not occur).
Let's consider the following setting:
A mixed file ProcessInfoProvider.mm, which calls [[NSProcessInfo processInfo] operatingSystemVersion] and provides the result in a C-style function std::string getProcessInfoVersion_C(),
A Pure cpp-file and a corresponding hpp-file UseProcessInfoInC.cpp/hpp defining a class MyCppProcessInfo, which provides a printVersion()-member function and which uses getProcessInfoVersion_C,
Some other file that instantiates MyCppProcessInfo and calls member function printVersion()
Let's start with ProcessInfoProvider.mm:
#import <Foundation/Foundation.h>
#import <Foundation/NSProcessInfo.h>
#include <string.h>
#include <iostream>
std::string getProcessInfoVersion_C (void) {
NSProcessInfo *processInfo = [[NSProcessInfo alloc] init];
// check avaiability of the property operatingSystemVersion (10.10+) at runtime
if ([processInfo respondsToSelector:#selector(operatingSystemVersion)])
{
NSOperatingSystemVersion versionObj = [processInfo operatingSystemVersion];
char version[500];
snprintf(version, 500, "Version %ld.%ld.%ld",
(long)versionObj.majorVersion,
(long)versionObj.minorVersion,
(long)versionObj.patchVersion);
return version;
}
else
{
// Implement fallback for OSX 10.9 and below
return "?";
}
}
Note that getProcessInfoVersion_C is a C-style function but contains objective-C code in it's implementation.
Then, pure C++ files UseProcessInfoInC.cpp/hpp implement class MyCppProcessInfo:
// UseProcessInfoInC.hpp:
#ifndef UseProcessInfoInC_hpp
#define UseProcessInfoInC_hpp
class MyCppProcessInfo {
public:
void printVersion(void);
};
#endif /* UseProcessInfoInC_hpp */
and
// UseProcessInfoInC.cpp:
#include "UseProcessInfoInC.hpp"
#include <iostream>
extern std::string getProcessInfoVersion_C (void);
void MyCppProcessInfo::printVersion(void)
{
std::string version = getProcessInfoVersion_C();
std::cout << version;
}
Note that these two files do not contain any Objective-C-stuff.
Finally, let's try out MyCppProcessInfo, e.g. in a function main():
// File main.mm
#import <UIKit/UIKit.h>
#import "AppDelegate.h"
#include "UseProcessInfoInC.hpp"
int main(int argc, char * argv[]) {
#autoreleasepool {
MyCppProcessInfo pi;
pi.printVersion();
return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
}
}