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NSOutputStream Class Reference

Overview

The NSOutputStream class is a subclass of NSStream that provides write-only stream functionality.

Subclassing Notes

The NSOutputStream is a concrete subclass of NSStream that lets you write data to a stream. Although NSOutputStream is probably sufficient for most situations requiring this capability, you can create a subclass of NSOutputStream if you want more specialized behavior (for example, you want to record statistics on the data in a stream).

Methods to Override

To create a subclass of NSOutputStream you may have to implement initializers for the type of stream data supported and suitably reimplement existing initializers. You must also provide complete implementations of the following methods:

• write:maxLength:

  From the current write pointer, take up to the number of bytes specified in the maxLength: parameter from the client-supplied buffer (first parameter) and put them onto the stream. The buffer must be of the size specified by the second parameter. To prepare for the next operation, offset the write pointer by the number of bytes written. Return a signed integer based on the outcome of the current operation:

  • If the write operation is successful, return the actual number of bytes put onto the stream.

  • If there was an error writing to the stream, return -1.

  • If the stream is of a fixed length and has reached its capacity, return zero.

• hasSpaceAvailable

  Return YES if the stream can currently accept more data, NO if it cannot. If you want to be semantically compatible with NSOutputStream, return YES if a write must be attempted to determine if space is available.

Tasks

Creating Streams

• + outputStreamToMemory
• + outputStreamToBuffer:capacity:
• + outputStreamToFileAtPath:append:
• – initToMemory
• – initToBuffer:capacity:
• – initToFileAtPath:append:

Using Streams

• – hasSpaceAvailable
• – write:maxLength:

Class Methods

outputStreamToBuffer:capacity:

Creates and returns an initialized output stream that can write to a provided buffer.

+ (id)outputStreamToBuffer:(uint8_t *)buffer capacity:(NSUInteger)capacity

Parameters

buffer

The buffer the output stream will write to.

capacity

The size of the buffer in bytes.

Return Value

An initialized output stream that can write to buffer.

Discussion

The stream must be opened before it can be used.

When the number of bytes written to buffer has reached capacity, the stream’s streamStatus will return NSStreamStatusAtEnd.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• + outputStreamToMemory
• + outputStreamToFileAtPath:append:
• – initToBuffer:capacity:

Declared In

NSStream.h

outputStreamToFileAtPath:append:

Creates and returns an initialized output stream for writing to a specified file.

+ (id)outputStreamToFileAtPath:(NSString *)path append:(BOOL)shouldAppend

Parameters

path

The path to the file the output stream will write to.

shouldAppend

YES if newly written data should be appended to any existing file contents, NO otherwise.

Return Value

An initialized output stream that can write to path.

Discussion

The stream must be opened before it can be used.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• + outputStreamToMemory
• + outputStreamToBuffer:capacity:
• – initToFileAtPath:append:

Declared In

NSStream.h

outputStreamToMemory

Creates and returns an initialized output stream that will write stream data to memory.

+ (id)outputStreamToMemory

Return Value

An initialized output stream that will write stream data to memory.

Discussion

The stream must be opened before it can be used.

You retrieve the contents of the memory stream by sending the message propertyForKey: to the receiver with an argument of NSStreamDataWrittenToMemoryStreamKey.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• + outputStreamToBuffer:capacity:
• + outputStreamToFileAtPath:append:
• – initToMemory

Declared In

NSStream.h

Instance Methods

hasSpaceAvailable

Returns whether the receiver can be written to.

- (BOOL)hasSpaceAvailable

Return Value

YES if the receiver can be written to or if a write must be attempted in order to determine if space is available, NO otherwise.

Availability

• Available in Mac OS X v10.3 and later.

Declared In

NSStream.h

initToBuffer:capacity:

Returns an initialized output stream that can write to a provided buffer.

- (id)initToBuffer:(uint8_t *)buffer capacity:(NSUInteger)capacity

Parameters

buffer

The buffer the output stream will write to.

capacity

The size of the buffer in bytes.

Return Value

An initialized output stream that can write to buffer.

Discussion

The stream must be opened before it can be used.

When the number of bytes written to buffer has reached capacity, the stream’s streamStatus will return NSStreamStatusAtEnd.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – initToMemory
• – initToFileAtPath:append:
• + outputStreamToBuffer:capacity:

Declared In

NSStream.h

initToFileAtPath:append:

Returns an initialized output stream for writing to a specified file.

- (id)initToFileAtPath:(NSString *)path append:(BOOL)shouldAppend

Parameters

path

The path to the file the output stream will write to.

shouldAppend

YES if newly written data should be appended to any existing file contents, NO otherwise.

Return Value

An initialized output stream that can write to path.

Discussion

The stream must be opened before it can be used.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – initToMemory
• – initToBuffer:capacity:
• + outputStreamToFileAtPath:append:

Declared In

NSStream.h

initToMemory

Returns an initialized output stream that will write to memory.

- (id)initToMemory

Return Value

An initialized output stream that will write stream data to memory.

Discussion

The stream must be opened before it can be used.

The contents of the memory stream are retrieved by passing the constant NSStreamDataWrittenToMemoryStreamKey to propertyForKey:.

Availability

• Available in Mac OS X v10.3 and later.

See Also

• – initToBuffer:capacity:
• – initToFileAtPath:append:
• + outputStreamToMemory

Declared In

NSStream.h

write:maxLength:

Writes the contents of a provided data buffer to the receiver.

- (NSInteger)write:(const uint8_t *)buffer maxLength:(NSUInteger)length

Parameters

buffer

The data to write.

length

The length of the data buffer, in bytes.

Return Value

The number of bytes actually written, or -1 if an error occurs. More information about the error can be obtained with streamError. If the receiver is a fixed-length stream and has reached its capacity, 0 is returned.

Availability

• Available in Mac OS X v10.3 and later.

Related Sample Code

• CocoaEcho

Declared In

NSStream.h

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