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我是 ios 新手，我有 10 个 1024 字节的块。这些块不按顺序排列。如果我知道块的数量，我如何将数据插入大小为 10*1024 的文件中？到目前为止，我有以下代码：

//method called when new chunk arrvies


 NSArray *paths = NSSearchPathForDirectoriesInDomains
    (NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    //create a file name to write the data to using the documents directory:
    filePath = [NSString stringWithFormat:@"%@/example.txt", 
                documentsDirectory];

    NSFileHandle *writeFile = [NSFileHandle fileHandleForWritingToURL:filePath error:nil];
    [writeFile truncateFileAtOffset:10240*sizeof(Byte)];

如何使用 fseek 添加新数据？

我确实尝试使用以下代码：

if ((chunkNo == 0 )||(chunkNo == 10))
    {
        NSOutputStream *stream = [[NSOutputStream alloc] initToFileAtPath:filePath append:YES];
        [stream open];
        NSData *chunk = chunkContainer; // some data
        [stream write:(uint8_t *)[chunk bytes] maxLength:[chunk length]];
        [stream close];

    }
    else{
        NSData *chunk = chunkContainer; // some data
        NSUInteger insertPoint = chunkNo*1024; // get the insertion point //
        // make sure the file exists, if it does, do the following //
        NSData *oldData = [NSData dataWithContentsOfFile:filePath];

        NSOutputStream *stream = [[NSOutputStream alloc] initToFileAtPath:filePath append:NO];
        [stream open];
        [stream write:(uint8_t *)[oldData bytes] maxLength:insertPoint]; // write the old data up to the insertion point //
         [stream write:(uint8_t *)[chunk bytes] maxLength:[chunk length]]; // write the new data //
         [stream write:(uint8_t *)([oldData bytes]+insertPoint) maxLength:([oldData length]-insertPoint)]; // write the rest of old data at the end of the file //

        [stream close];
    }

但是如果块的顺序不正确，结果文件并不完全正确。如果块的顺序正确，则结果文件将正确显示。

4

2 回答 2

4

例子：

NSString *filePath = [@"~/Desktop/FHTest.txt" stringByExpandingTildeInPath];

[[NSFileManager defaultManager] createFileAtPath:filePath contents:[NSData new] attributes:nil];
NSFileHandle *fh;

NSData *data1 = [@"test Data" dataUsingEncoding:NSUTF8StringEncoding];
fh = [NSFileHandle fileHandleForUpdatingAtPath:filePath];
[fh writeData:data1];
[fh closeFile];

NSData *data2 = [@"more Data" dataUsingEncoding:NSUTF8StringEncoding];
fh = [NSFileHandle fileHandleForUpdatingAtPath:filePath];
[fh seekToFileOffset:100];
[fh writeData:data2];
[fh closeFile];

请注意，seekToFileOffset:100将根据需要填充扩展文件，并根据需要使用 0x00 字节填充。

要创建特定大小的文件，在本例中为 100 字节：

unsigned long long size = 100;
[[NSFileManager defaultManager] createFileAtPath:filePath contents:[NSData new] attributes:nil];
NSFileHandle *fh = [NSFileHandle fileHandleForUpdatingAtPath:filePath];
[fh seekToFileOffset:size-1];
[fh writeData:[@"\x00" dataUsingEncoding:NSUTF8StringEncoding]];
[fh closeFile];
于 2014-06-24T13:18:01.857 回答
0

关于问题的第一部分（我是如何到达这里的），如果您只想要一个特定大小的空文件......

[[NSData dataWithBytes:@[] length:size] writeToFile:path atomically:false];
于 2020-11-19T22:18:41.733 回答