The open procedure


The open procedure associates a file variable with a file (i.e. opens the file variable and allows it to be used to manipulate the file). The open procedure can open the file variable in read-only mode, write-only mode, read/write mode, or append mode.


  1. The first parameter is a reference to the file variable to be opened.
  2. The second parameter is an expression of string type or char type, and names the file variable, referenced by the first parameter, as if the built-in procedure assign had been called.
  3. The third parameter is an expression of integral type which specifies the mode the file variable should be opened in. The file mode constants can be used to specify the mode. The readmode and writemode constants can be added or OR'd together to specify that the file variable be opened in read/write mode (i.e. for both reading and writing).
The name of the file variable, referenced by the first parmater, controls which file is opened by the open procedure. If the name is a non-empty string then a file with that name is opened. If the name is an empty string then the file opened is either the standard output file, or a temporary file (with a system generated name), depending on the project options set when the program was compiled.

File variables can get named in the following ways:


   open(f, 'filename', readmode);   //this is the same as reset(f, 'filename');
   open(f, 'filename', writemode); //this is the same as rewrite(f, 'filename');
   open(f, 'filename', appendmode); //this is the same as append(f, 'filename');

The following call to open

   open(f, 'test.txt', readmode+writemode);

will open the file 'test.txt in read/write mode (i.e. for both reading and writing).


Operating Systems: All
Standard Pascal: No