Question

我正在为iphone学习目标c并遇到一些小错误：

控制台输出：

kill
quit

The Debugger has exited with status 0.
[Session started at 2011-04-26 17:51:40 -0700.]
GNU gdb 6.3.50-20050815 (Apple version gdb-1510) (Wed Sep 22 02:45:02 UTC 2010)
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This GDB was configured as "x86_64-apple-darwin".tty /dev/ttys000
Loading program into debugger…
Program loaded.
run
[Switching to process 13334]
2011-04-26 17:51:40.788 RandomPossessions[13334:a0f] Two
2011-04-26 17:51:40.792 RandomPossessions[13334:a0f] Three
2011-04-26 17:51:40.793 RandomPossessions[13334:a0f] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (4) beyond bounds (4)'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x00007fff81d007b4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x00007fff856730f3 objc_exception_throw + 45
    2   CoreFoundation                      0x00007fff81d005d7 +[NSException raise:format:arguments:] + 103
    3   CoreFoundation                      0x00007fff81d00564 +[NSException raise:format:] + 148
    4   Foundation                          0x00007fff88ef6aa0 _NSArrayRaiseBoundException + 122
    5   Foundation                          0x00007fff88e59bc5 -[NSCFArray objectAtIndex:] + 75
    6   RandomPossessions                   0x0000000100000e8d main + 301
    7   RandomPossessions                   0x0000000100000d58 start + 52
    8   ???                                 0x0000000000000001 0x0 + 1
)
terminate called after throwing an instance of 'NSException'
Running…
Program received signal:  “SIGABRT”.
sharedlibrary apply-load-rules all
(gdb)

我的代码：

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    // insert code here...
    NSMutableArray *items = [[NSMutableArray alloc] init];

    [items addObject:@"One"];
    [items addObject:@"Two"];
    [items addObject:@"Three"];
    [items insertObject:@"Zero" atIndex:0];

    for(int i=0 <[items count];i++;)
    {
        NSLog(@"%@", [items objectAtIndex:i]);
    }

    [pool drain];
    return 0;
}

我认为程序应该输出零，一，二，三。

这里发生了什么？

Answer 1

您写道：

for(int i=0 <[items count];i++;)

那是一个错字吗？它应该是：

for(int i=0; i<[items count]; i++)

Answer 2

for (NSString item in items) {
    NSLog(@"%@", item);
}

客观c课程的简单问题

2 个答案: