try-except in Delphi

Three strings through StrToInt, one of them not a number, handled instead of crashing.

program TryExcept;
uses SysUtils;
procedure Report(const Raw: string);
var Minutes: Integer;
begin
  try
    Minutes := StrToInt(Raw);  // raises EConvertError on junk input
    WriteLn(Format('%-6s %3d min', [Raw, Minutes]));
  except
    on E: EConvertError do     // on-do names the class and the instance
      WriteLn(Format('%-6s skipped: %s', [Raw, E.Message]));
  end;
end;
begin
  Report('45');
  Report('4o');  // the handler runs, then the program carries on
  Report('12');
end.

How it works

1. Minutes := StrToInt(Raw) raises EConvertError when the text is not an integer.
2. on E: EConvertError do catches that one class and binds the instance to E.
3. Report('4o') prints E.Message and the calls after it still run.

Keywords and builtins used here

• Format
• Integer
• Report
• StrToInt
• WriteLn
• begin
• const
• do
• end
• except
• on
• procedure
• program
• string
• try
• uses
• var

The run, in numbers

Lines

18

Characters to type

460

Tokens

97

Three-star pace

75 tpm

At the three-star pace of 75 tokens a minute, this run takes about 78 seconds.

Type this snippet

Step 2 of 3 in Exceptions, step 23 of 27 in Language basics.

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