object-c学习：类的静态成员

初学咋练难免惹笑话，有错误处拍砖哈 :-)

object-c中并没有提供类静态变量，只能以文件作用域的static变量代替，然后由类的成员函数来操作，这样设计的目的，还没想明白，先mark下以后再说把。下面提供个例子：

#import <Foundation/Foundation.h>

static int sTier_count = 0;

@interface Tier : NSObject 
{
@private
    int tier_num;
}
@end

@implementation Tier
- (id) init
{
    if (self = [super init]) {
        sTier_count++;
        tier_num = sTier_count;
    }

    return self;
}

- (void) release
{
    if (sTier_count > 0) {
        sTier_count--;
    }
}

- (NSString*) description
{
    return [NSString stringWithFormat:
            @"i'm a tier, my number is %d", tier_num];
}
@end

@interface Engine : NSObject
@end

@implementation Engine
- (NSString*) description
{
    return (@"i'm a engine");
}
@end

@interface Car : NSObject
{
    Engine* engine;
    Tier* tiers[4];
}
@end

@implementation Car
- (id) init
{
    if (self = [super init]) {
        engine = [Engine new];
        int i = 0;
        for (; i<4; i++) {
            tiers[i] = [Tier new];
        }
    }

    return self;
}

- (NSString*) description
{
    return ("@I'm a car");
}

- (void) print
{
    int i = 0;
    for(; i<4; i++) {
        NSLog(@"%@", tiers[i]);
    }
    NSLog(@"%@", engine);
}
@end

int main(char argc, char* argv[]) {
    Car* car = [Car new];
    [car print];

    return 0;
}