RegExpr matchting empty string

[fred]

Hello,

When I try to match a empty string with a a regular expression like this:

Code: Pascal  [Select][+][-]

1.   writeln(RegExpr.ExecRegExpr('^$', ''));

I get als result: false
I expected this to be true, what am I doing wrong?

Tried also the TRExExpr class with property EmptyInputRaisesError true of false but still got an error with a empty expression.

I must be getting old

Fred.
Lazarus 4.6/fpc 3.2.2

[Martin_fr]

It seems to work with 3.3.1.

Or get the upstream regex project.

[Thaddy]

I get true with trunk:

Code: Pascal  [Select][+][-]

1. // full program
2. uses regexpr;
3. begin
4.   writeln(RegExpr.ExecRegExpr('^$', ''));// returns TRUE
5. end.

Afaik, the upstream is compatible with 3.2.2, though.

[fred]

Thanks Martin and Thaddy.

I took a quick look at regexpr.pas from 3.2.2 and 3.3.1 but did not see much difference in OP_BOL/OP_EOL.

My complete test program was:

Code: Pascal  [Select][+][-]

1. {$mode objfpc} {$H+}
2.  
3. uses sysutils, strutils, RegExpr;
4.  
5. begin
6.   writeln(RegExpr.ExecRegExpr(ParamStr(1), ParamStr(2)));
7.   writeln(RegExpr.ExecRegExpr('^$', ''));
8. end.
9.  

Running with InstantFPC.
So much like the one from Thaddy.
Strange...

For now I have made a workaround, when I have more time I will try to take a deeper look (like always "when more time"...).

Fred.

[Thausand]

pascal

Code: Pascal  [Select][+][-]

1. {$mode objfpc} {$H+}
2. uses sysutils, strutils, RegExpr;
3. begin
4.   writeln(RegExpr.ExecRegExpr('^$', ''));
5. end.
6.  

3.2.2

Code: Bash  [Select][+][-]

1. $ fpc-332 -B test.pas
2. Free Pascal Compiler version 3.2.2 [2024/10/24] for x86_64
3. Copyright (c) 1993-2021 by Florian Klaempfl and others
4. Target OS: Linux for x86-64
5. Compiling test.pas
6. Linking test
7. 8 lines compiled, 0.1 sec
8. $ ./test
9. TRUE
10.  

3.3.1

Code: Bash  [Select][+][-]

1. $ fpc331 -B test.pas
2. Free Pascal Compiler version 3.3.1 [2025/03/01] for x86_64
3. Copyright (c) 1993-2025 by Florian Klaempfl and others
4. Target OS: Linux for x86-64
5. Compiling test.pas
6. Linking test
7. 8 lines compiled, 0.2 sec, 795008 bytes code, 370912 bytes data
8. $ ./test
9. TRUE
10.  

[Thaddy]

@Fred

There is an error in your code that causes an exception:
If the params array does not have paramstr(1),paramstr(2) the program crashes.
To fix, use paramcount:

Code: Pascal  [Select][+][-]

1. // full program
2. uses RegExpr;
3. begin
4.   if paramcount >= 2 then  // check!!!
5.   begin
6.     writeln(RegExpr.ExecRegExpr(ParamStr(1), ParamStr(2)));
7.     writeln(RegExpr.ExecRegExpr('^$', ''));
8.   end;
9. end.

Paramstr(0), the executable name, is not counted towards paramcount.
That may be all. With two or more "''"  (empty)  parameters this prints true, true, otherwise prints false where the parameters are filled or otherwise does nothing.

(The double quotes are just illustrating, use '' or "" (two quotes of the same type))

BTW: not a bug: maps to argc/argv.
(which is a ppointer to an array of PChar closed with a double zero.)

[fred]

Thanks Thaddy.

I know, it was just a small test program.
Since I did not get it to work in a GUI program I made is back to the smallest program I could test.
I still make and like to use small command line tools since FLEX/6809, UniFLEX, OS-9/68k, want to write the line editor I used then

I used the regex for searching in a grid, with testing I could not find an empty cell with '^$'.
For know I use:

Code: Pascal  [Select][+][-]

1.         if ((zoektekst = '^$') and (Cells[c, r] = ''))
2.         or RegexObj.Exec(Cells[c, r])
3.  

Not how I like it but it works.
When I have more time (...) I would test it using the debugger or install another version of the compiler.
An empty search string is not possible using FindDialog so that doesn't happen.
Or just make a search function for empty cells, would be a little faster.
It's for myself so not a problem.

Thanks all.

Edit:
Checked it on https://onecompiler.com/pascal/44jxcj6jz
and the result is TRUE
Interesting

Edit2:
Running in https://webflow.replit.com/language/online-pascal-compiler
and the result is FALSE
Very Interesting

Fred.

[Thaddy]

@Fred

For the online compilers, try

Code: Pascal  [Select][+][-]

1. program whoami;
2. // full program
3. var
4.   id:array[0..1023] of char;external name '__fpc_ident';
5. begin
6.   writeln(id);
7. end.

The first link crashes and shows fpc 3.0.4 in its dump:

Code: Text  [Select][+][-]

1. Free Pascal Compiler version 3.0.4 [2017/10/03] for x86_64
2. Copyright (c) 1993-2017 by Florian Klaempfl and others
3. Target OS: Linux for x86-64
4. Compiling main.pas
5. Linking main
6. /usr/bin/ld: warning: link.res contains output sections; did you forget -T?
7. /usr/bin/ld: main.o: in function `main':
8. main.pas:(.text.n_main+0x1c): undefined reference to `__fpc_ident'
9. main.pas(7,1) Error: Error while linking
10. main.pas(7,1) Fatal: There were 1 errors compiling module, stopping
11. Fatal: Compilation aborted
12. Error: /usr/local/fpc-3.0.4/bin/ppcx64 returned an error exitcode

The second link passes and shows "FPC 3.2.2 [2024/05/14] for x86_64 - Linux"

I would trust the second link......

(The ID works from 3.2.0, but undocumented!!!)

[Thaddy]

Official, documented and serverside non-crashing version:

Code: Pascal  [Select][+][-]

1. program whoami;
2. {$macro on}
3. begin
4.   writeln(fpc_fullversion);
5.   writeln(fpc_version,fpc_release,fpc_patch);
6. end.

But that gives a bit less info.