binary file

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Binary file

A binary file is suitable for processing files of any size. With binary files, the content of a file is read in character by character. Conversely, the file is written character by character. If a file is opened as a binary file, a character can be changed anywhere in the file. Data of the same type can now be written and read into a file defined with FILE OF as follows:

 var
   datFile : File of Byte;    // always reads and writes a character
   datFile : File of Char;    // always reads and writes a character
   datFile : File of Integer; // always reads and writes two characters
   ...

Any location in the binary file can be accessed with the SEEK command.

Create file

 var
   datFile    : File of Char;
   chrContent : Char;

 begin
   Assignfile(datFile, 'example.txt');  // Assigns the name of the file to the variable txtFile and opens the file
   ReWrite(datFile);                    // File will be overwritten if it exists
   chrContent := 'A';
   Write(datFile, chrContent);          // Write the first character to the new file 
   ...
 end;

Close file

 var
   datFile    : File of Char;
   chrContent : Char;

 begin
   ...
   CloseFile(datFile);  // closes the file
 end;

Add a character to the end of an existing file

For binary files, a character can be added to the end of a file using the Seek command.

 var
   datFile    : File of char;
   chrContent : Char;

 begin
   AssignFile(datFile, 'example.txt');
   Reset(datFile);                    // Sets the file pointer to the beginning of the file
   Seek(datFile, FileSize(datFile));  // Determines the end of the file and sets the file pointer to the end
   chrContent := 'b';
   Write(datFile, chrContent);        // Write another character at the end of the file
   ...

Replace a character in an existing file

For binary files, you can use the Seek command to replace a character anywhere in the file.

 var
   datFile    : File of Char;
   chrContent : Char;

 begin
   AssignFile(datFile, 'example.txt');
   Reset(datFile);                     // Sets the file pointer to the beginning of the file
   Seek (datFile, 1);                  // Set the file pointer to the _second_ character in the file
   chrContent := 'f';
   Write(datFile, chrContent);         // Overwrite the second character in the file
   ...

Read file completely

 var
   datFile    : File of Char;
   chrContent : Char;

 begin
   AssignFile(datFile, 'example.txt');
   Reset(datFile);
   
   while not eof(datFile)           // keep reading as long as there is data to read
     do begin
       read(datFile, chrContent);   // reads a single character into chrContent variable
       ...
     end;

   CloseFile(datFile);
 end;

See also

File types