NSMutableData mutableBytes
- (void *)mutableBytes
Return Value
A pointer to the receiver’s data.
Discussion of [NSMutableData mutableBytes]
If the length of the receiver’s data is not zero, this function is guaranteed to return a pointer to the object's internal bytes. If the length of receiver’s data is zero, this function may or may not return NULL dependent upon many factors related to how the object was created (moreover, in this case the method result might change between different releases).
A sample using this method can be found in Working With Mutable Binary Data.
NSMutableData mutableBytes example.
NSMutableData* mydata = [[NSMutableData alloc] init];
[mydata appendData: [@"hello" dataUsingEncoding:NSUTF8StringEncoding]];
NSLog(@"%p", [mydata mutableBytes]);
NSLog(@"%p", [mydata bytes]);
[mydata appendData: [@"hello" dataUsingEncoding:NSUTF8StringEncoding]];
NSLog(@"%p", [mydata mutableBytes]);
NSLog(@"%p", [mydata bytes]);
Example of [NSMutableData mutableBytes].
typedef struct {
UInt32 riffChunkID; // Always RIFF, in big endian. Integer fields are little-ending.
UInt32 fileLength;
UInt32 waveFileID; // 'WAVE' for Wave files.
UInt32 formatChunkID; // 'fmt '
UInt32 formatChunkSize;
SInt16 formatTag; // Wave Format ID: see constants
SInt16 channels; // Number of Channels: 1=mono, 2=stereo
SInt32 sampleRate; // Sample Rate: samples per second
SInt32 bytesPerSec; // sampleRate * blockAlign
SInt16 blockAlign; // sample frame size = channels * sampleSize / 8
SInt16 bitsPerSample; // sampleSize (8 or 16), also two's-complement for 16-bit, offset for 8-bit
UInt32 dataChunkID; // 'data'
UInt32 dataChunkSize;
} WaveHeader;
int tfChannels = 1; // mono
int tfSampleRate = 44100;
int tfBitsPerSample = 16;
WaveHeader *header = [maindata mutableBytes];
header->riffChunkID = CFSwapInt32HostToBig ('RIFF');
header->fileLength = CFSwapInt32HostToLittle ([maindata length] - 8);
header->waveFileID = CFSwapInt32HostToBig ('WAVE');
header->formatChunkID = CFSwapInt32HostToBig ('fmt ');
header->formatChunkSize = CFSwapInt32HostToLittle (16);
header->formatTag = CFSwapInt16HostToLittle (1);
header->channels = CFSwapInt16HostToLittle (tfChannels);
header->sampleRate = CFSwapInt32HostToLittle (tfSampleRate);
header->bytesPerSec = CFSwapInt32HostToLittle (tfSampleRate * tfBitsPerSample / 8 * tfChannels);
header->blockAlign = CFSwapInt16HostToLittle (tfBitsPerSample / 8 * tfChannels);
header->bitsPerSample = CFSwapInt16HostToLittle (tfBitsPerSample);
header->dataChunkID = CFSwapInt32HostToBig ('data');
header->dataChunkSize = CFSwapInt32HostToLittle ([maindata length] - 44);
UInt32 riffChunkID; // Always RIFF, in big endian. Integer fields are little-ending.
UInt32 fileLength;
UInt32 waveFileID; // 'WAVE' for Wave files.
UInt32 formatChunkID; // 'fmt '
UInt32 formatChunkSize;
SInt16 formatTag; // Wave Format ID: see constants
SInt16 channels; // Number of Channels: 1=mono, 2=stereo
SInt32 sampleRate; // Sample Rate: samples per second
SInt32 bytesPerSec; // sampleRate * blockAlign
SInt16 blockAlign; // sample frame size = channels * sampleSize / 8
SInt16 bitsPerSample; // sampleSize (8 or 16), also two's-complement for 16-bit, offset for 8-bit
UInt32 dataChunkID; // 'data'
UInt32 dataChunkSize;
} WaveHeader;
int tfChannels = 1; // mono
int tfSampleRate = 44100;
int tfBitsPerSample = 16;
WaveHeader *header = [maindata mutableBytes];
header->riffChunkID = CFSwapInt32HostToBig ('RIFF');
header->fileLength = CFSwapInt32HostToLittle ([maindata length] - 8);
header->waveFileID = CFSwapInt32HostToBig ('WAVE');
header->formatChunkID = CFSwapInt32HostToBig ('fmt ');
header->formatChunkSize = CFSwapInt32HostToLittle (16);
header->formatTag = CFSwapInt16HostToLittle (1);
header->channels = CFSwapInt16HostToLittle (tfChannels);
header->sampleRate = CFSwapInt32HostToLittle (tfSampleRate);
header->bytesPerSec = CFSwapInt32HostToLittle (tfSampleRate * tfBitsPerSample / 8 * tfChannels);
header->blockAlign = CFSwapInt16HostToLittle (tfBitsPerSample / 8 * tfChannels);
header->bitsPerSample = CFSwapInt16HostToLittle (tfBitsPerSample);
header->dataChunkID = CFSwapInt32HostToBig ('data');
header->dataChunkSize = CFSwapInt32HostToLittle ([maindata length] - 44);
NSMutableData mutableBytes example.
NSMutableData* mutableData = [NSMutableData dataWithLength: someLength];
void* bitmapData = [mutableData mutableBytes];
CGContextRef context = CGBitmapContextCreate(bitmapData,...);
// ...use context
CGContextRelease(context);
void* bitmapData = [mutableData mutableBytes];
CGContextRef context = CGBitmapContextCreate(bitmapData,...);
// ...use context
CGContextRelease(context);