C语言 attribute的问题

对于你的问题不太明白。

#define __init_call __attribute__ ((unused,__section__ (".initcall.init ")))

参考GCC说明，意思是说所有以__init_call前缀定义的函数在链接过程中都放到名字为.initcall.init的段（section）里面。也就是说，如果一个函数冠以__init_call，那么它在编译链接的时候就会放到.initcall.init这个段里面。

第一种：runtime.h里的方法BOOL class_addProperty(Class cls,const char *name, const objc_property_attribute_t *attributes,unsigned int attributeCount) #include <objc/runtime.h> #import <Foundation/Foundation.h> @interface SomeClass : NSObject { NSString *_privateName}@end@implementation SomeClass- (id)init { self = [super init] if (self) _privateName = @"Steve" return self}@endNSString *nameGetter(id self, SEL _cmd) { Ivar ivar = class_getInstanceVariable([SomeClass class], "_privateName") return object_getIvar(self, ivar)} void nameSetter(id self, SEL _cmd, NSString *newName) { Ivar ivar = class_getInstanceVariable([SomeClass class], "_privateName") id oldName = object_getIvar(self, ivar) if (oldName != newName) object_setIvar(self, ivar, [newName copy])}int main(void) { @autoreleasepool {objc_property_attribute_t type = { "T", "@/"NSString/"" } objc_property_attribute_t ownership = { "C", "" }// C = copy objc_property_attribute_t backingivar = { "V", "_privateName" } objc_property_attribute_t attrs[] = { type, ownership, backingivar } class_addProperty([SomeClass class], "name", attrs, 3) class_addMethod([SomeClass class], @selector(name), (IMP)nameGetter, "@@:") class_addMethod([SomeClass class], @selector(setName:), (IMP)nameSetter, "v@:@") id o = [SomeClass new] NSLog(@"%@", [o name]) [o setName:@"Jobs"] NSLog(@"%@", [o name]) }}输出：SteveJobs 第二种：- (id)valueForUndefinedKey:(NSString *)key 第三种：static char const * const ObjectTagKey@implementation NSObject (ExampleCategoryWithProperty)@dynamic objectTag- (id)objectTag { return objc_getAssociatedObject(self, ObjectTagKey) } - (void)setObjectTag:(id)newObjectTag { objc_setAssociatedObject(self, ObjectTagKey, newObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC)}

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