How to check for blank entry (enter key)

[nugax]

I have an if statement checking for #10 for an enter key pressed , but it doesn't seem to work. Any ideas?

[nugax]

I said #10 I meant I am checking for #13

[Handoko]

Please show us the code.

[taazz]

as far as I remember about readln, it does not return the enter key to the variable read from the keyboard, you need to clean the keyboard buffer after each readln to clean up the ln portion of the read operation. You simply check for empty string usually after a trim operation to avoid being tricked from a space or control characters.

[Handoko]

@nugax

To do like what taazz said, try something like this:

Code: Pascal  [Select][+][-]

1. if S = '' then ... // do something

or

Code: Pascal  [Select][+][-]

1. if S.Trim = '' then ... // do something

[Thaddy]

or even simpler:

Code: Pascal  [Select][+][-]

1. if s.IsEmpty then //

Note a space can be valid input, so depending on application you may want to simply test for length(s)=0, which is what IsEmpty does.

In a Lazarus GUI application it is much simpler: edit controls listen to VK_RETURN, eg:

Code: Pascal  [Select][+][-]

1. // make sure lcltype is in the uses clause!!
2. procedure TForm1.Edit1KeyUp(Sender: TObject; var Key: Word; Shift: TShiftState);
3. begin
4.   if Key = VK_RETURN then Caption := 'Enter/Return pressed';
5. end;

Note this is cross-platform too...
Console apps have an inferred LineEding when using ReadLn, like:

Code: Pascal  [Select][+][-]

1. program keytest;
2. {$ifdef fpc}{$mode delphi}{$H+}{$I-}{$endif}
3. uses sysutils;
4. var
5.   s:string;
6. begin
7.   writeln('Press somekeys or not, then press enter');
8.   readln(s);  // LineEnding is always inferred when using ReadLn...
9.   if s.IsEmpty then writeln('Empty') else writeln('NotEmpty: ',s);
10. end.

[nugax]

@nugax

To do like what taazz said, try something like this:

Code: Pascal  [Select][+][-]

1. if S = '' then ... // do something

or

Code: Pascal  [Select][+][-]

1. if S.Trim = '' then ... // do something

Is S a string? I do not have a trim option on a string[255];

[Handoko]

Trim and IsEmpty and other String Helper functions  are provided by unit SysUtils, so you need to add SysUtils into your uses clause.

https://www.freepascal.org/docs-html/rtl/sysutils/tstringhelper.html

[nugax]

Trim and IsEmpty and other String Helper functions  are provided by unit SysUtils, so you need to add SysUtils into your uses clause.

https://www.freepascal.org/docs-html/rtl/sysutils/tstringhelper.html

I have sysutils, but for some reason Trim doesnt work.

[nugax]

Trim and IsEmpty and other String Helper functions  are provided by unit SysUtils, so you need to add SysUtils into your uses clause.

https://www.freepascal.org/docs-html/rtl/sysutils/tstringhelper.html

I have sysutils, but for some reason Trim doesnt work.

I figured it out! Thanks!