After "upgrading" to macOS High Sierra it seems that some code that used to work does no longer. My goal here is just to list out the windows owned by an application. Here is an example:
#import <Foundation/Foundation.h>
#import <CoreFoundation/CoreFoundation.h>
#import <ApplicationServices/ApplicationServices.h>
int main(int argc, const char * argv[]) {
#autoreleasepool {
pid_t myPID = 311;
AXUIElementRef appRef = AXUIElementCreateApplication(myPID);
CFArrayRef windowList;
AXUIElementCopyAttributeValue(appRef, kAXWindowsAttribute, (CFTypeRef *)&windowList);
}
return 0;
}
The issue here specifically is that windowList does not get contain anything no matter what I do. I have tried multiple PIDs, building/running both debug and release builds, and running them with sudo as well.
Any ideas?
I have the following objective-c snippet in my hello world example:
//hello.m
#import <Foundation/Foundation.h>
#import "hello.h"
void sayHello()
{
#ifdef FRENCH
NSString *helloWorld = #"Bonjour Monde!\n";
#else
NSString *helloWorld = #"Hello World\n";
#endif
printf("%s", [helloWorld UTF8String]);
}
//main.m
#import <Foundation/Foundation.h>
#import "hello.h"
int main (int argc, const char * argv[])
{
sayHello();
return 0;
}
building this stuff on osx works fine and runs as expected. But when compiling/linking it on ubuntu (using GNUStep) results in an segmentation fault when executing the binary. I nailed it down to the casting operation in the printf statement, but I have no clue what I'm doing wrong here or how I can solve this.
Interesting note: This works fine when using gcc toolchain to build the executable. I just see this issue when building it with clang on ubuntu.
Any help is very much appreciated.
To fix this issue, I ended up changing my code to the following:
...
void sayHello()
{
#ifdef FRENCH
NSString *helloWorld = #"${HELLO_WORLD_FRENCH}\\n";
#else
NSString *helloWorld = #"${HELLO_WORLD}\\n";
#endif
NSFileHandle *stdout = [NSFileHandle fileHandleWithStandardOutput];
NSData *strData = [helloWorld dataUsingEncoding: NSASCIIStringEncoding];
[stdout writeData: strData];
}
...
This could sound a bit weird.
In main.m, it is written as such:
int main(int argc, char * argv[])
{
#autoreleasepool {
return UIApplicationMain(argc, argv, nil, NSStringFromClass([RTAppDelegate class]));
}
}
which is a C-style main function (though with typical [class method] function call). But if we look at syntax of objective-C, one might think of something like this:
+(int)main:(int)argc :(char*) argv[] //I don't really know if (char*) argv[] will be legit in obj-c
{
// DO SOMETHING
return 0;
}
So I'm getting confused about the language itself. Does objective-c simply extends C-syntax? Or is it an independent language itself?
Objective-C is a superset of C. As such, you can (or at least, should be able to) compile any C program through an Objective-C compiler.
Knowing this, the ANSI C standard states that the correct declaration of main is either int main(int argc, char** argv) or int main(void).
http://c-faq.com/ansi/maindecl.html
I can't figure out why I get
use of undeclared identifier _cmd did you mean rcmd
on the line where NSAssert is.
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
int x = 10;
NSAssert(x > 11, #"x should be greater than %d", x);
[pool drain];
return 0;
}
Inside every Objective-c method there are two hidden variables id self and SEL _cmd
so
- (void)foo:(id)bar;
is really
void foo(id self, SEL _cmd, id bar) { ... }
and when you call
[someObject foo:#"hello world"]
it is actually
foo( someObject, #selector(foo), #"hello world")
If you cmd-click on NSAssert to jump to it's definition you will see that it is a macro that uses the hidden _cmd variable of the method you are calling it from. This means that if you are not inside an Objective-c method (perhaps you are in 'main'), therefore you don't have a _cmd argument, you cannot use NSAssert.
Instead you can use the alternative NSCAssert.
NSAssert is only meant to be used within Objective-C methods. Since main is a C function, use NSCAssert instead.
Try to replace
NSAssert(x > 11, [NSString stringWithFormat:#"x should be greater than %d", x]);
with
NSCAssert(x > 11, [NSString stringWithFormat:#"x should be greater than %d", x]);
You have to wrap your string in a NSString class if you want to use format parameters. That is because #"" is a default constructor for a plain NSString. The way it is written now gives a third parameter to the NSAssert function and messes with it.
NSAssert(x > 11, [NSString stringWithFormat:#"x should be greater than %d", x]);
TL;DR - stick with stray NSAssert() - don't try this in production
Original code
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
int x = 10;
NSAssert(x > 11, #"x should be greater than %d", x);
[pool drain];
return 0;
}
Build failure
Compiling file hello.m ...
hello.m:9:5: error: use of undeclared identifier '_cmd'
NSAssert(x > 11, #"x should be greater than %d", x);
^
/usr/include/Foundation/NSException.h:450:32: note: expanded from macro 'NSAssert'
handleFailureInMethod: _cmd \
^
hello.m:9:5: error: use of undeclared identifier 'self'
/usr/include/Foundation/NSException.h:451:17: note: expanded from macro 'NSAssert'
object: self \
^
2 errors generated.
Based on explanation by #hooleyhoop #Robert and
id
self
SEL,
the following dirty hack may be applicable if I insist on using
NSAssert() instead of
NSCAssert()
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
int x = 10;
// Dirty hack
SEL _cmd=NULL;
NSObject *self=NULL;
NSAssert(x > 11, #"x should be greater than %d", x);
[pool drain];
return 0;
}
Build & run
Compiling file hello.m ...
Linking tool hello ...
2021-03-04 21:25:58.035 hello[39049:39049] hello.m:13 Assertion failed in (null)(instance), method (null). x should be greater than 10
./obj/hello: Uncaught exception NSInternalInconsistencyException, reason: hello.m:13 Assertion failed in (null)(instance), method (null). x should be greater than 10
Hooray it works! But, alas, please stay away from it :)
The following code compiles fine ...
int main (int argc, const char * argv[]) {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// VARIABLES
MDD *MDD_structure;
NSString *mddFile = #"/Users/Gary/Code/Mdd/xTest.mdd";
NSFileHandle *inFile;
NSData *inBuffer;
int MDD_fCount;
int MDD_vCount;
// OPEN FILE ON DISK
inFile = [NSFileHandle fileHandleForReadingAtPath:mddFile];
if(inFile == nil) NSLog(#"FILE: Open ... ERROR");
else NSLog(#"FILE: Open ... OK");
// READ FRAME COUNT
inBuffer = [inFile readDataOfLength:sizeof(int)];
[inBuffer getBytes:&MDD_fCount length:sizeof(int)];
MDD_fCount = CFSwapInt32BigToHost(MDD_fCount);
NSLog(#"FC: %d", MDD_fCount);
But when I run it through the static analyzer "CLANG LLVM 1.0" I get the following ...
warning: Pass-by-value argument in function call is undefined.
MDD_fCount = CFSwapInt32BigToHost(MDD_fCount);
^ ~~~~~~~~~~
1 diagnostic generated.
Can anyone tell me what I am missing?
gary
You're getting an error because clang isn't convinced that simply passing the address of your variable to a function is the same as giving it a value. You could probably initialize MDD_fCount to 0 to start with to get rid of the error.
It means that you haven't initialized MDD_fCount. See this blog post and this other question for additional info.