使用宏定义创建单例

//单例

#ifndef KCSingleton_h
#define KCSingleton_h

#pragma mark 接口.h中的定义
//由于宏定义里有需要替换的内容所以定义一个变量className
//##用于分割、连接字符串
#define singleton_interface(className) +(className *)shared##className;

#pragma mark 实现.m
//在代码中用于连接宏定义,以实现多行定义
#define singleton_implementation(className) 
static className *_instance;
+(id)shared##className{
    if(!_instance){
        _instance=[[self alloc]init];
    }
    return _instance;
}
+(id)allocWithZone:(struct _NSZone *)zone{
    static dispatch_once_t dispatchOnce;
    dispatch_once(&dispatchOnce, ^{
        _instance=[super allocWithZone:zone];
    });
    return _instance;
}

#endif