Objective-C 源码初探 __attribute__

#import <Foundation/Foundation.h>
#define onExit\
    __strong void (^block)() __attribute__((cleanup(cleanup),unused)) = ^

__attribute__((constructor)) void ExecuteBefore_main(){
    printf("ExecuteBefore_main\n");
}

__attribute__((destructor)) void ExecuteAfter_main(){
    printf("ExecuteAfter_main\n");
}

void functionDeprecatedAndObsoleteWarningAndError() __attribute__ ((availability(macosx,introduced=10.4,deprecated=10.10,obsoleted=10.13)));

void functionDeprecatedAndObsoleteWarningAndError(void){

}

int returnValueNotUnusedWarning() __attribute__ ((warn_unused_result));

int returnValueNotUnusedWarning(){
    return 1;
}

void cleanup(__strong void (^*block)()){
    (*block)();
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {

        printf("Hello, World!\n");

        functionDeprecatedAndObsoleteWarningAndError();
        returnValueNotUnusedWarning();
        onExit{
            printf("onExit\n");
        };
    }
    return 0;
}