blitz-research
65 lines
4.6 KiB
HTML
65 lines
4.6 KiB
HTML
<html><head><title>Command: ReadByte </title><meta http-equiv='Content-Type' content='text/html; charset=iso-8859-1'><link rel='stylesheet' href='../css/commands.css' type='text/css'></head><body><span class='Command'> ReadByte ( filehandle|stream ) </span></p><span class='header'>Definition:</span> <br><br><table width='100%' border='0' cellspacing='2' cellpadding='2' align='center'><tr><td>Reads a single byte of data from an open file (or stream) and returns it as an integer value between 0 and 255.</td></tr></table><span class='header'><br>Parameter Description:</span> <br><br><table width='100%' border='0' cellspacing='2' cellpadding='2' align='center'><tr><td>filehandle|stream = a valid variable set with the OpenFile, ReadFile command, or OpenTCPStream (v1.52+)</td></tr></table><p class='header'>Command Description: <br><br><table width='100%' border='0' cellspacing='2' cellpadding='2' align='center'><tr><td>Once you've opened a disk file (or stream) for reading, use this command to read a single byte at a time from the file/stream. Note, a byte is an integer that can take the values 0..255 and occupies 8 bits of storage. Since characters are stored as byte values this function can be used to read a file one character at a time. Reading beyond the end of file does not result in an error, but each value read will be zero.<br>
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<br>
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Advanced notes<br>
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<br>
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The number that is stored by WriteByte is actually the least significant byte of an integer so negative numbers and numbers above 255 will still have a value between 0..255. Unless you understand how 32 bit integers are stored in 2's compliment notation this will seem strange but it is NOT a
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bug.<br>
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<br>
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Streams can only be used in Blitz Basic v1.52 or greater.
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See also:<br>
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<a href='ReadByte.htm'>ReadByte</a>, <a href='ReadShort.htm'>ReadShort</a>, <a href='ReadInt.htm'>ReadInt</a>, <a href='ReadFloat.htm'>ReadFloat</a>, <a href='ReadString$.htm'>ReadString$</a>, <a href='ReadLine$.htm'>ReadLine$</a>, <a href='WriteByte.htm'>WriteByte</a>, <a href='WriteShort.htm'>WriteShort</a>, <a href='WriteInt.htm'>WriteInt</a>, <a href='WriteFloat.htm'>WriteFloat</a>, <a href='WriteShort.htm'>WriteShort</a>, <a href='WriteString.htm'>WriteString</a>, <a href='WriteLine.htm'>WriteLine</a>, <a href='ReadFile.htm'>ReadFile</a>, <a href='WriteFile.htm'>WriteFile</a>, <a href='OpenFile.htm'>OpenFile</a>, <a href='CloseFile.htm'>CloseFile</a>, <a href='Eof.htm'>Eof</a>, <a href='FileType.htm'>FileType</a>, <a href='FilePos.htm'>FilePos</a>, <a href='SeekFile.htm'>SeekFile</a></td></tr></table><p class='header'>Example: <br><br><table width='100%' border='0' cellspacing='2' cellpadding='2' align='center'><tr><td>; Reading and writing a file using ReadByte and WriteByte functions<br>
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<br>
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; Initialise some variables for the example<br>
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Byte1% = 10 ; store 10<br>
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Byte2% = 100 ; store 100<br>
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Byte3% = 255 ; store 255 ( the maximum value that can be stored in a Byte)<br>
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Byte4% = 256 ; try to store 256 this will end up as 0 ( i.e. 256 - 256 = 0 )<br>
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Byte5% = 257 ; try to store 257 this will end up as 1 ( i.e. 257 - 256 = 1 )<br>
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Byte6% = -1 ; try to store -1 this will end up as 255 ( i.e. 256 -1 = 255 )<br>
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Byte7% = -2 ; try to store 256 this will end up as 254 ( i.e. 256 - 2 = 254 )<br>
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Byte8% = Asc("A") ; Store the ASCII value for the Character "A" ( i.e. 65 )<br>
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<br>
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; Open a file to write to<br>
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fileout = WriteFile("mydata.dat ")<br>
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<br>
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; Write the information to the file<br>
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WriteByte( fileout, Byte1 )<br>
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WriteByte( fileout, Byte2 )<br>
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WriteByte( fileout, Byte3 )<br>
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WriteByte( fileout, Byte4 )<br>
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WriteByte( fileout, Byte5 )<br>
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WriteByte( fileout, Byte6 )<br>
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WriteByte( fileout, Byte7 )<br>
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WriteByte( fileout, Byte8 )<br>
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<br>
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; Close the file<br>
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CloseFile( fileout )<br>
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<br>
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; Open the file to Read<br>
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filein = ReadFile("mydata.dat")<br>
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<br>
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Read1 = ReadByte( filein )<br>
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Read2 = ReadByte( filein )<br>
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Read3 = ReadByte( filein )<br>
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Read4 = ReadByte( filein )<br>
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Read5 = ReadByte( filein )<br>
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Read6 = ReadByte( filein )<br>
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Read7 = ReadByte( filein )<br>
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Read8 = ReadByte( filein )<br>
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<br>
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; Close the file once reading is finished<br>
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CloseFile( fileout )<br>
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<br>
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Print "Written - Read"<br>
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Write Byte1 + " - " : Print Read1<br>
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Write Byte2 + " - " : Print Read2<br>
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Write Byte3 + " - " : Print Read3<br>
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Write Byte4 + " - " : Print Read4<br>
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Write Byte5 + " - " : Print Read5<br>
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Write Byte6 + " - " : Print Read6<br>
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Write Byte7 + " - " : Print Read7<br>
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Write Byte8 + " - " : Print Chr$( Read8 )<br>
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<br>
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WaitKey()<br></td></tr></table><p><b><a target="_top" href="../index.htm">Index</a></b></p></body>
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</html>
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