我试图将我的一些 Objective-C 项目从 GCC 切换到 Linux 上的 Clang。我使用了 GCC 4.6.2 运行时，因为 Clang 编译器没有附带一个。编译和链接工作，但使用protocol_*方法时，它们不起作用。
以下示例适用于 GCC，但不适用于 Clang：
#include <objc/runtime.h>
#include <stdio.h>
@protocol MyProtocol
+ aClassMethod;
- anInstanceMethod;
@end
void doIt(Protocol *p, SEL sel)
{
printf("the protocol: %p\n", p);
if (!p) return;
printf("the protocol's name: %s\n", protocol_getName(p));
struct objc_method_description d = protocol_getMethodDescription(p, sel, YES, YES);
printf("required: YES instance: YES → %p\n", d.name);
d = protocol_getMethodDescription(p, sel, YES, NO);
printf("required: YES instance: NO → %p\n", d.name);
d = protocol_getMethodDescription(p, sel, NO, YES);
printf("required: NO instance: YES → %p\n", d.name);
d = protocol_getMethodDescription(p, sel, NO, NO);
printf("required: NO instance: NO → %p\n", d.name);
}
int main(int argc, char **argv)
{
Protocol *p1 = @protocol(MyProtocol);
printf("P1\n");
printf("class method first:\n");
doIt(p1, @selector(aClassMethod));
printf("instance method follows:\n");
doIt(p1, @selector(anInstanceMethod));
Protocol *p2 = objc_getProtocol("MyProtocol");
printf("P2\n");
printf("class method first:\n");
doIt(p2, @selector(aClassMethod));
printf("instance method follows:\n");
doIt(p2, @selector(anInstanceMethod));
printf("done\n");
return 0;
}
GCC 编译程序的预期输出：
P1
class method first:
the protocol: 0x804a06c
the protocol's name: MyProtocol
required: YES instance: YES → (nil)
required: YES instance: NO → 0x804b530
required: NO instance: YES → (nil)
required: NO instance: NO → (nil)
instance method follows:
the protocol: 0x804a06c
the protocol's name: MyProtocol
required: YES instance: YES → 0x804b528
required: YES instance: NO → (nil)
required: NO instance: YES → (nil)
required: NO instance: NO → (nil)
P2
class method first:
the protocol: 0x804a06c
the protocol's name: MyProtocol
required: YES instance: YES → (nil)
required: YES instance: NO → 0x804b530
required: NO instance: YES → (nil)
required: NO instance: NO → (nil)
instance method follows:
the protocol: 0x804a06c
the protocol's name: MyProtocol
required: YES instance: YES → 0x804b528
required: YES instance: NO → (nil)
required: NO instance: YES → (nil)
required: NO instance: NO → (nil)
done
Clang 编译程序的意外输出：
P1
class method first:
the protocol: 0x804a050
the protocol's name: (null)
required: YES instance: YES → (nil)
required: YES instance: NO → (nil)
required: NO instance: YES → (nil)
required: NO instance: NO → (nil)
instance method follows:
the protocol: 0x804a050
the protocol's name: (null)
required: YES instance: YES → (nil)
required: YES instance: NO → (nil)
required: NO instance: YES → (nil)
required: NO instance: NO → (nil)
P2
class method first:
the protocol: (nil)
instance method follows:
the protocol: (nil)
done
这里有什么问题？是否有一些神奇的初始化代码在使用 Clang 时不会被调用？
[更新]
当添加如下协议的实现时，该objc_getProtocol()方法有效，但protocol_*方法仍然无效。
@interface MyInstance <MyProtocol>
@end
@implementation MyInstance
+ aClassMethod
{
return nil;
}
- anInstanceMethod
{
return nil;
}
@end