我是ios新手 我有 10 个 1024 字节的 block 。这些 block 不按顺序排列。 如果我知道 block 的数量,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 block 的顺序不正确,则结果文件不完全正确。如果 block 的顺序正确,则结果文件将正确显示。
最佳答案
示例:
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,并根据需要填充 0x00 字节。
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];
关于ios - 创建一个特定大小的空文件并使用 fseek 将新数据写入特定位置,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24386858/