[SOLVED] Improvement of function SetCompileModeSwitch
lazarus / 64-FPC development

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lagprogramming · 2023-11-19 07:33

compiler/scanner.pas has function SetCompileModeSwitch(s:string;
changeInit: boolean):boolean;
Within the code of the function "s:=copy(s,1,length(s)-1);" can be
encountered twice. The attached patch replaces it with
"setlength(s,length(s)-1);".

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AlexTP · 2023-11-19 07:56

Reported to
https://gitlab.com/freepascal.org/fpc/source/-/issues/40525

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vangli · 2023-11-19 08:12

Hi. Just of curriosity. Isn't it?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
s:=copy(s,1,length(s)-1);
will guaranty that "s" is minimum an empty string if it happens that
"s" is single byte or already an empty string.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
setlength(s,length(s)-1);
will release memory if "s" is one byte long or already an empty
string. Then the rest of the function SetCompileModeSwitch will crash?

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TRon · 2023-11-19 08:34

Quote from: vangli on November 19, 2023, 09:12:35 amwill release
memory if "s" is one byte long or already an empty string. Then the
rest of the function SetCompileModeSwitch will crash?
Nah, not really 

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i case
s[length(s)] of

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vangli · 2023-11-19 08:53

Thks TRon. I may have been (mis)leaded by
https://www.freepascal.org/docs-html/rtl/system/setlength.html where
it states the following:

"Note that SetLength is governed by the Copy-On-Write principle for
strings and dynamic arrays: the reference count after a call to
SetLength will be 1 (except when the length is zero, then the array is
removed from memory). "

I read the parenthesis to include both strings and arrays, but it may
only be true for array length.