Mega Code Archive
Blockwrite - writes a block of data records to an untyped binary file system unit
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procedure BlockWrite ( var FileHandle : File; var Buffer; RecordCount : Integer {; var RecordsWritten : Integer} ) ;
Description
The BlockWrite procedure is used to write to RecordCount data records from Buffer to an untyped binary file given by the FileHandle.
The file must have been assigned using AssignFile and opened with Reset or ReWrite.
The Reset and ReWrite routines by default will open the file with a record size of 128 bytes. This can be overriden in these routines to a value more useful to yourself (see example).
Data is taken from the Buffer (normally a string or byte array) and written to the file. If the recordSize is 10 bytes, and RecordCount is 3, then 3 x 10 byte records are written, with 30 bytes taken from the buffer to do this.
The actual number of records written is stored in the optional RecordsWritten variable, if provided. It may be les than RecordCount if, for example, the hard disk was full.
Related commands
BlockRead Reads a block of data records from an untyped binary file
File Defines a typed or untyped file
Read Read data from a binary or text file
ReadLn Read a complete line of data from a text file
Write Write data to a binary or text file
WriteLn Write a complete line of data to a text file
Example code : Writing three 4-byte records in 2 block write to a binary file.
var
myFile : File;
byteArray : array[1..8] of byte;
oneByte : byte;
i, count : Integer;
begin
// Try to open the Test.byt file for writing to
AssignFile(myFile, 'Test.byt');
ReWrite(myFile, 4); // Define a single 'record' as 4 bytes
// Fill out the data array
for i := 1 to 8 do
byteArray[i] := i;
// Write the data array to the file
BlockWrite(myFile, byteArray, 2); // Write 2 'records' of 4 bytes
// Fill out the data array with different data
for i := 1 to 4 do
byteArray[i] := i*i; // Value : 1, 4, 9, 16
// Write only the first 4 items from the data array to the file
BlockWrite(myFile, byteArray, 1); // Write 1 record of 4 bytes
// Close the file
CloseFile(myFile);
// Reopen the file for reading only
FileMode := fmOpenRead;
Reset(myFile, 1); // Now we define one record as 1 byte
// Display the file contents
// Start with a read of the first 6 bytes. 'count' is set to the
// actual number read
ShowMessage('Reading first set of bytes :');
BlockRead(myFile, byteArray, 6, count);
// Display the byte values read
for i := 1 to count do
ShowMessage(IntToStr(byteArray[i]));
// Now read one byte at a time to the end of the file
ShowMessage('Reading remaining bytes :');
while not Eof(myFile) do
begin
BlockRead(myFile, oneByte, 1); // Read and display one byte at a time
ShowMessage(IntToStr(oneByte));
end;
// Close the file for the last time
CloseFile(myFile);
end;
Show full unit code
Reading first set of bytes :
1
2
3
4
5
6
Reading remaining bytes :
7
8
1
4
9
16
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