BlitzMax/Modules/Streams/Streams

Streams are used to read or write data in a sequential manner. BlitzMax supports many kinds of streams, including standard file streams (for reading and writing to files), bank streams (for reading and writing to banks) and endian streams (for swapping the byte order of stream data). Streams are usually created using OpenStream, ReadStream or WriteStream. However, some kinds of streams provide their own methods for creating streams. For example, banks streams are created with the CreateBankStream command. OpenStream, ReadStream and WriteStream all require a url parameter, which is used to 'locate' the stream. A url is usually a string value. If the url contains the string "::", then a stream protocol is being specified. If not, then the url is assumed to be a simple filename. External modules can add their own stream protocols to the system, allowing you to use streams for a wide variety of purposes. For example, the "incbin::" protocol allows you to read data from a binary file that has been embedded in an application using the Incbin command. Other protocols include "http::" for reading and writing data over a network, and "littleendian::" and "bigendian::" for swapping the byte order of streams. To write to a stream, use one of the 'Write' style commands, such as WriteByte. To read from a stream, use one of the 'Read' style commands, such as ReadByte. Some kinds of streams (for example, file streams and bank streams) support random access. This means that you can modify where in the stream the next read or write is to occur using the SeekStream command. You can also tell where you are in such streams using the StreamPos command. When you are finished with a stream, you should always close it using CloseStream. Failure to do so may result in a resource leak, or prevent the stream from successfully opening in future. Types TStreamException Base exception type thrown by streams TStreamReadException Exception type thrown by streams in the event of read errors TStreamReadException is usually thrown when a stream operation failed to read enough bytes. For example, if the stream ReadInt method fails to read 4 bytes, it will throw a TStreamReadException. TStreamWriteException Exception type thrown by streams in the event of write errors TStreamWriteException is usually thrown when a stream operation failed to write enough bytes. For example, if the stream WriteInt method fails to write 4 bytes, it will throw a TStreamWriteException. TIO Base input/output type To create your own stream types, you should extend TStream and implement at least these methods. You should also make sure your stream can handle multiple calls to the Close method. Methods Eof Pos Size Seek Flush Close Read Write TIO: Methods Eof Method Eof() Description: Get stream end of file status Returns: True for end of file reached, otherwise False Information: For seekable streams such as file streams, Eof generally returns True if the file position equals the file size. This means that no more bytes can be read from the stream. However, it may still be possible to write bytes, in which case the file will 'grow'. For communication type streams such as socket streams, Eof returns True if the stream has been shut down for some reason - either locally or by the remote host. In this case, no more bytes can be read from or written to the stream. Pos Method Pos() Description: Get position of seekable stream Returns: Stream position as a byte offset, or -1 if stream is not seekable Size Method Size() Description: Get size of seekable stream Returns: Size, in bytes, of seekable stream, or 0 if stream is not seekable Seek Method Seek( pos ) Description: Seek to position in seekable stream Returns: New stream position, or -1 if stream is not seekable Flush Method Flush() Description: Flush stream Information: Flushes any internal stream buffers. Close Method Close() Description: Close stream Information: Closes the stream after flushing any internal stream buffers. Read Method Read( buf:Byte Ptr,count ) Description: Read at least 1 byte from a stream Returns: Number of bytes successfully read Information: This method may 'block' if it is not possible to read at least one byte due to IO buffering. If this method returns 0, the stream has reached end of file. Write Method Write( buf:Byte Ptr,count ) Description: Write at least 1 byte to a stream Returns: Number of bytes successfully written Information: This method may 'block' if it is not possible to write at least one byte due to IO buffering. If this method returns 0, the stream has reached end of file. TStream Data stream type TStream extends TIO to provide methods for reading and writing various types of values to and from a stream. Note that methods dealing with strings - ReadLine, WriteLine, ReadString and WriteString - assume that strings are represented by bytes in the stream. In future, a more powerful TextStream type will be added capable of decoding text streams in multiple formats. Methods ReadBytes WriteBytes SkipBytes ReadByte WriteByte ReadShort WriteShort ReadInt WriteInt ReadLong WriteLong ReadFloat WriteFloat ReadDouble WriteDouble ReadLine WriteLine ReadString WriteString TStream: Methods ReadBytes Method ReadBytes( buf:Byte Ptr,count ) Description: Reads bytes from a stream Information: ReadBytes reads count bytes from the stream into the memory block specified by buf. If count bytes were not successfully read, a TStreamReadException is thrown. This typically occurs due to end of file. WriteBytes Method WriteBytes( buf:Byte Ptr,count ) Description: Writes bytes to a stream Information: WriteBytes writes count bytes from the memory block specified by buf to the stream. If count bytes were not successfully written, a TStreamWriteException is thrown. This typically occurs due to end of file. SkipBytes Method SkipBytes( count ) Description: Skip bytes in a stream Information: SkipBytes read count bytes from the stream and throws them away. If count bytes were not successfully read, a TStreamReadException is thrown. This typically occurs due to end of file. ReadByte Method ReadByte() Description: Read a byte from the stream Returns: The read value Information: If a value could not be read (possibly due to end of file), a TStreamReadException is thrown. WriteByte Method WriteByte( n ) Description: Write a byte to the stream Information: If the value could not be written (possibly due to end of file), a TStreamWriteException is thrown. ReadShort Method ReadShort() Description: Read a short (two bytes) from the stream Returns: The read value Information: If a value could not be read (possibly due to end of file), a TStreamReadException is thrown. WriteShort Method WriteShort( n ) Description: Write a short (two bytes) to the stream Information: If the value could not be written (possibly due to end of file), a TStreamWriteException is thrown. ReadInt Method ReadInt() Description: Read an int (four bytes) from the stream Returns: The read value Information: If a value could not be read (possibly due to end of file), a TStreamReadException is thrown. WriteInt Method WriteInt( n ) Description: Write an int (four bytes) to the stream Information: If the value could not be written (possibly due to end of file), a TStreamWriteException is thrown. ReadLong Method ReadLong:Long() Description: Read a long (eight bytes) from the stream Returns: The read value Information: If a value could not be read (possibly due to end of file), a TStreamReadException is thrown. WriteLong Method WriteLong( n:Long ) Description: Write a long (eight bytes) to the stream Information: If the value could not be written (possibly due to end of file), a TStreamWriteException is thrown. ReadFloat Method ReadFloat#() Description: Read a float (four bytes) from the stream Returns: The read value Information: If a value could not be read (possibly due to end of file), a TStreamReadException is thrown. WriteFloat Method WriteFloat( n# ) Description: Write a float (four bytes) to the stream Information: If the value could not be written (possibly due to end of file), a TStreamWriteException is thrown. ReadDouble Method ReadDouble!() Description: Read a double (eight bytes) from the stream Returns: The read value Information: If a value could not be read (possibly due to end of file), a TStreamReadException is thrown. WriteDouble Method WriteDouble( n! ) Description: Write a double (eight bytes) to the stream Information: If the value could not be written (possibly due to end of file), a TStreamWriteException is thrown. ReadLine Method ReadLine$() Description: Read a line of text from the stream Information: Bytes are read from the stream until a newline character (ascii code 10) or null character (ascii code 0) is read, or end of file is detected. Carriage return characters (ascii code 13) are silently ignored. The bytes read are returned in the form of a string, excluding any terminating newline or null character. WriteLine Method WriteLine( str$ ) Description: Write a line of text to the stream Returns: True if line successfully written, else False Information: A sequence of bytes is written to the stream (one for each character in str) followed by the line terminating sequence "~r~n". ReadString Method ReadString$( length ) Description: Read characters from the stream Returns: A string composed of length bytes read from the stream Information: A TStreamReadException is thrown if not all bytes could be read. WriteString Method WriteString( str$ ) Description: Write characters to the stream Information: A TStreamWriteException is thrown if not all bytes could be written. TStreamWrapper Utility stream wrapper type TStreamWrapper 'wraps' an existing stream, redirecting all TIO method calls to the wrapped stream. This can be useful for writing stream 'filters' that modify the behaviour of existing streams. Note that the Close method causes the underlying stream to be closed, which may not always be desirable. If necessary, you should override Close with a NOP version. Methods SetStream TStreamWrapper: Methods SetStream Method SetStream( stream:TStream ) Description: Set underlying stream Information: Sets the stream to be 'wrapped'. All calls to TIO methods of this stream will be redirected to stream. TCStream Standard C file stream type Functions OpenFile CreateWithCStream TCStream: Functions OpenFile Function OpenFile:TCStream( path$,readable,writeable ) Description: Create a TCStream from a 'C' filename CreateWithCStream Function CreateWithCStream:TCStream( cstream,mode ) Description: Create a TCStream from a 'C' stream handle TStreamFactory Base stream factory type Stream factories are used by the OpenStream, ReadStream and WriteStream functions to create streams based on a 'url object'. Url objects are usually strings, in which case the url is divided into 2 parts - a protocol and a path. These are separated by a double colon string - "::". To create your own stream factories, you should extend the TStreamFactory type and implement the CreateStream method. To install your stream factory, simply create an instance of it using 'New'. Methods CreateStream TStreamFactory: Methods CreateStream Method CreateStream:TStream( url:Object,proto$,path$,readable,writeable ) Description: Create a stream based on a url object Information: Types which extends TStreamFactory must implement this method. url contains the original url object as supplied to OpenStream, ReadStream or WriteStream. If url is a string, proto contains the url protocol - for example, the "incbin" part of "incbin::myfile". If url is a string, path contains the remainder of the url - for example, the "myfile" part of "incbin::myfile". If url is not a string, both proto and path will be Null. Functions OpenStream Function OpenStream:TStream( url:Object,readable=True,writeable=True ) Description: Open a stream for reading/writing Returns: A stream object Information: All streams created by OpenStream, ReadStream or WriteStream should eventually be closed using CloseStream. ReadStream Function ReadStream:TStream( url:Object ) Description: Open a stream for reading Returns: A stream object Information: All streams created by OpenStream, ReadStream or WriteStream should eventually be closed using CloseStream. Example: ' readstream.bmx ' opens a read stream to the blitzbasic.com website and ' dumps the homepage to the console using readline and print in=ReadStream("http::blitzbasic.com") If Not in RuntimeError "Failed to open a ReadStream to file http::www.blitzbasic.com" While Not Eof(in) Print ReadLine(in) Wend CloseStream in WriteStream Function WriteStream:TStream( url:Object ) Description: Open a stream for writing Returns: A stream object Information: All streams created by OpenStream, ReadStream or WriteStream should eventually be closed using CloseStream. Example: ' writestream.bmx ' opens a write stream to the file mygame.ini and ' outputs a simple text file using WriteLine out=WriteStream("mygame.ini") if not out RuntimeError "Failed to open a WriteStream to file mygame.ini" WriteLine out,"[display]" WriteLine out,"width=800" WriteLine out,"height=600" WriteLine out,"depth=32" WriteLine out,"" WriteLine out,"[highscores]" WriteLine out,"AXE=1000" WriteLine out,"HAL=950" WriteLine out,"MAK=920" CloseStream out print "File mygame.ini created, bytes="+FileSize("mygame.ini") Eof Function Eof( stream:TStream ) Description: Get stream end of file status Returns: True If stream is at end of file StreamPos Function StreamPos( stream:TStream ) Description: Get current position of seekable stream Returns: Current stream position, or -1 If stream is not seekable StreamSize Function StreamSize( stream:TStream ) Description: Get current size of seekable stream Returns: Current stream size in bytes, or -1 If stream is not seekable SeekStream Function SeekStream( stream:TStream,pos ) Description: Set stream position of seekable stream Returns: New stream position, or -1 If stream is not seekable FlushStream Function FlushStream( stream:TStream ) Description: Flush a stream Information: FlushStream writes any outstanding buffered data to stream. CloseStream Function CloseStream( stream:TStream ) Description: Close a stream Information: All streams should be closed when they are no longer required. Closing a stream also flushes the stream before it closes. ReadByte Function ReadByte( stream:TStream ) Description: Read a Byte from a stream Returns: A Byte value Information: ReadByte reads a single Byte from stream. A TStreamReadException is thrown If there is not enough data available. ReadShort Function ReadShort( stream:TStream ) Description: Read a Short from a stream Returns: A Short value Information: ReadShort reads 2 bytes from stream. A TStreamReadException is thrown If there is not enough data available. ReadInt Function ReadInt( stream:TStream ) Description: Read an Int from a stream Returns: An Int value Information: ReadInt reads 4 bytes from stream. A TStreamReadException is thrown If there is not enough data available. ReadLong Function ReadLong:Long( stream:TStream ) Description: Read a Long from a stream Returns: A Long value Information: ReadLong reads 8 bytes from stream. A TStreamReadException is thrown If there is not enough data available. ReadFloat Function ReadFloat#( stream:TStream ) Description: Read a Float from a stream Returns: A Float value Information: ReadFloat reads 4 bytes from stream. A TStreamReadException is thrown If there is not enough data available. ReadDouble Function ReadDouble!( stream:TStream ) Description: Read a Double from a stream Returns: A Double value Information: ReadDouble reads 8 bytes from stream. A TStreamWriteException is thrown If there is not enough data available. WriteByte Function WriteByte( stream:TStream,n ) Description: Write a Byte to a stream Information: WriteByte writes a single Byte to stream. A TStreamWriteException is thrown If the Byte could Not be written WriteShort Function WriteShort( stream:TStream,n ) Description: Write a Short to a stream Information: WriteShort writes 2 bytes to stream. A TStreamWriteException is thrown if not all bytes could be written WriteInt Function WriteInt( stream:TStream,n ) Description: Write an Int to a stream Information: WriteInt writes 4 bytes to stream. A TStreamWriteException is thrown if not all bytes could be written WriteLong Function WriteLong( stream:TStream,n:Long ) Description: Write a Long to a stream Information: WriteLong writes 8 bytes to stream. A TStreamWriteException is thrown if not all bytes could be written WriteFloat Function WriteFloat( stream:TStream,n# ) Description: Write a Float to a stream Information: WriteFloat writes 4 bytes to stream. A TStreamWriteException is thrown if not all bytes could be written WriteDouble Function WriteDouble( stream:TStream,n! ) Description: Write a Double to a stream Information: WriteDouble writes 8 bytes to stream. A TStreamWriteException is thrown if not all bytes could be written ReadString Function ReadString$( stream:TStream,length ) Description: Read a String from a stream Returns: A String of length length Information: A TStreamReadException is thrown if not all bytes could be read. WriteString Function WriteString( stream:TStream,str$ ) Description: Write a String to a stream Information: Each character in str is written to stream. A TStreamWriteException is thrown if not all bytes could be written. ReadLine Function ReadLine$( stream:TStream ) Description: Read a line of text from a stream Returns: A string Information: Bytes are read from stream until a newline character (ascii code 10) or null character (ascii code 0) is read, or end of file is detected. Carriage Return characters (ascii code 13) are silently ignored. The bytes read are returned in the form of a string, excluding any terminating newline or null character. WriteLine Function WriteLine( stream:TStream,str$ ) Description: Write a line of text to a stream Returns: True if line successfully written, else False Information: A sequence of bytes is written to the stream (one for each character in str) followed by the line terminating sequence "~r~n". LoadString Function LoadString$( url:Object ) Description: Load a String from a stream Returns: A String Information: The specified url is opened for reading, and each byte in the resultant stream (until eof of file is reached) is read into a string. A TStreamReadException is thrown if the stream could not be read. SaveString Function SaveString( str$,url:Object ) Description: Save a String to a stream Information: The specified url is opened For writing, and each character of str is written to the resultant stream. A TStreamWriteException is thrown if not all bytes could be written. LoadByteArray Function LoadByteArray:Byte[]( url:Object ) Description: Load a Byte array from a stream Returns: A Byte array Information: The specified url is opened for reading, and each byte in the resultant stream (until eof of reached) is read into a byte array. SaveByteArray Function SaveByteArray( byteArray:Byte[],url:Object ) Description: Save a Byte array to a stream Information: The specified url is opened For writing, and each element of byteArray is written to the resultant stream. A TStreamWriteException is thrown if not all bytes could be written. CopyStream Function CopyStream( fromStream:TStream,toStream:TStream,bufSize=4096 ) Description: Copy stream contents to another stream Information: CopyStream copies bytes from fromStream to toStream Until fromStream reaches end of file. A TStreamWriteException is thrown if not all bytes could be written. CopyBytes Function CopyBytes( fromStream:TStream,toStream:TStream,count,bufSize=4096 ) Description: Copy bytes from one stream to another Information: CopyBytes copies count bytes from fromStream to toStream. A TStreamReadException is thrown if not all bytes could be read, and a TStreamWriteException is thrown if not all bytes could be written. CasedFileName Function CasedFileName$(path$) Description: Returns a case sensitive filename if it exists from a case insensitive file path.