1. CS 2
2/25/2015
File Exists?

2. Learning Objectives
Be able to determine if a file exists before trying to reset the file
Write a program using files

3. Checking if a file exists
function FileExists(FileName:string):Boolean;
{It returns TRUE if the file exists; otherwise, it returns FALSE. It closes the file if it exists.}
var
DummyFile: file;
Begin
{$I-} {This turns off the error detection for file handling}
Assign(DummyFile, FileName);
Reset(DummyFile);
Close(DummyFile);
{$I+} {This turns the error checking back on}
FileExists:= (IOResult = 0) and (FileName <>’’);
End;

4. Some Pascal File Error Codes IOResult
2: writeln('File not found');
3: writeln('Path not found');
4: writeln('Too many open files');
5: writeln('File access denied');
100: writeln('Disk read error');
101: writeln('Disk write error');
150: writeln('Disk is write protected');
152: writeln('Drive is not ready');
154: writeln('CRC error in data');
156: writeln('Disk seek error');
157: writeln('Unknown media type');
162: writeln('Hardware failure');
else writeln('Various error');

5. Example without declarations
function FileExists(FileName: string):Boolean;
{It returns TRUE if the file exists; otherwise, it returns FALSE. It closes the file if it exists.}
var
DummyFile: file;
Begin
{$I-} {This turns off the error detection for file handling}
Assign(DummyFile, FileName);
Reset(DummyFile);
Close(DummyFile);
{$I+} {This turns the error checking back on}
FileExists:= (IOResult = 0) and (FileName <>’’);
End;
If FileExists(‘stuff.dta’) then
Writeln(‘The file exists and can be opened with the reset command’);
Else
Writeln(‘The file does not exist’);
End.
Can use any string.

6. To do today and Friday
Using what you have learned about files, write a program with the following…
Menu
Create a new file
Check to see if it exists before this
Show all the names from the file
Check to see if it exists
Find if a name is in the file
Check
Add to an existing file.
Quit
Push: Let the user pick the file name.
Push: Make a file of records to store the name and phone number
Push: Sort the information in the file.