Strange and Random Access Violations

[Ugochukwu Mmaduekwe 42]

Hi all,

I wrote a simple function to help me convert a string to an array of char but I keep getting random occurring access violations.

 

class function TUtilities.StringToCharArray(const S: String)
  : TCharArray;
begin
  if System.Length(S) > 0 then
  begin
    System.SetLength(Result, System.Length(S));
    StrPLCopy(PChar(Result), S, System.Length(Result));
  end;
end;

Anyone know the cause?

Thanks.

[Attila Kovacs 617]

it's in the help

 

Note: Dest should point to a location with room for MaxLen + 1 characters, including the null terminator.

 

too bad that the compiler can't detect the out of range

Edited November 21, 2018 by Attila Kovacs

[Guest]

You should try this

class function TUtilities.StringToCharArray(const S: String)
  : TCharArray;
begin
  System.SetLength(Result, System.Length(S));
  if System.Length(S) > 0 then
  begin
    StrPLCopy(PChar(Result), S, System.Length(Result));
  end;
end;

 

[Ugochukwu Mmaduekwe 42]

5 hours ago, Attila Kovacs said:

it's in the help

 

Note: Dest should point to a location with room for MaxLen + 1 characters, including the null terminator.

 

too bad that the compiler can't detect the out of range

Thanks a lot, this did solve the problem.

[Ugochukwu Mmaduekwe 42]

35 minutes ago, Schokohase said:

You should try this

class function TUtilities.StringToCharArray(const S: String)
  : TCharArray;
begin
  System.SetLength(Result, System.Length(S));
  if System.Length(S) > 0 then
  begin
    StrPLCopy(PChar(Result), S, System.Length(Result));
  end;
end;

 

unfortunately, this did not work, but thanks either way.

[David Heffernan 2293]

You write a zero byte beyond the end of the char array. Solve the problem by using Move to perform the copy. 

[KodeZwerg 54]

*removed, error*

 

Edited November 21, 2018 by KodeZwerg

[KodeZwerg 54]

2 hours ago, Ugochukwu Mmaduekwe said:

System.SetLength(Result, System.Length(S));

This should be  SetLength(Result, Length(S) * SizeOf( AnsiChar ) );
 

program Project1;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;


function MyStringToMyCharArray( const S: String ): TCharArray;
begin
  SetLength(Result, Length(S) * SizeOf( AnsiChar ) );
  if Length( S ) > 0 then
  begin
    StrPLCopy( PChar( Result ), S, Length( Result ) );
  end;
end;


var
 S: String;
 C: TCharArray;
 I: Integer;
begin
  try
    { TODO -oUser -cConsole Main : Insert code here }
    S := 'My Test String';
    C := MyStringToMyCharArray( S );
    for i := 0 to Length( C ) -1 do
      write( c[ i ] );
    writeln;
    readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

 

Edited November 21, 2018 by KodeZwerg

[Kryvich 163]

function StringToCharArray(const S: string): TCharArray;
begin
  PChar(Result) := PChar(S);
end;

 

[Guest]

Option 1

uses
  System.SysUtils;
  
class function TUtilities.StringToCharArray(const S: String)
  : TCharArray;
begin
  Result := S.ToCharArray();
end;

Option 2 (found at System.SysUtils.TStringHelper.ToCharArray from Delphi 10.2.3 Tokyo)

class function TUtilities.StringToCharArray(const S: String)
  : TCharArray;
begin
  SetLength(Result, Length(S));
  Move(PChar(PChar(S))^, Result[0], Length(S) * SizeOf(Char));
end;

 

Edited November 21, 2018 by Guest

[Ugochukwu Mmaduekwe 42]

43 minutes ago, KodeZwerg said:

This should be  SetLength(Result, Length(S) * SizeOf( AnsiChar ) );
 

program Project1;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;


function MyStringToMyCharArray( const S: String ): TCharArray;
begin
  SetLength(Result, Length(S) * SizeOf( AnsiChar ) );
  if Length( S ) > 0 then
  begin
    StrPLCopy( PChar( Result ), S, Length( Result ) );
  end;
end;


var
 S: String;
 C: TCharArray;
 I: Integer;
begin
  try
    { TODO -oUser -cConsole Main : Insert code here }
    S := 'My Test String';
    C := MyStringToMyCharArray( S );
    for i := 0 to Length( C ) -1 do
      write( c[ i ] );
    writeln;
    readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

 

This will give the same access violation as the previous one if you run it multiple times in a loop.

The +1 space for the null terminator still applies.

[Ugochukwu Mmaduekwe 42]

26 minutes ago, Kryvich said:

function StringToCharArray(const S: string): TCharArray;
begin
  PChar(Result) := PChar(S);
end;

 

Oddly enough, this seems to work.

Another function in my arsenal.

Thanks.

[Fritzew 51]

45 minutes ago, KodeZwerg said:

This should be  SetLength(Result, Length(S) * SizeOf( AnsiChar ) );

Can you tell us why you think these is right? There is no reason for this construct. 
Length(s) is enough .

[Ugochukwu Mmaduekwe 42]

8 minutes ago, Schokohase said:

Option 1

uses
  System.SysUtils;
  
class function TUtilities.StringToCharArray(const S: String)
  : TCharArray;
begin
  Result := S.ToCharArray();
end;

Option 2 (found at System.SysUtils.TStringHelper.ToCharArray)

class function TUtilities.StringToCharArray(const S: String)
  : TCharArray;
begin
  SetLength(Result, Length(S));
  Move(PChar(PChar(S))^, Result[0], Length(S) * SizeOf(Char));
end;

 

Thanks but am trying to avoid the string helper functions, I also want to avoid using *move* on strings because I heard some time back that it breaks reference counting on strings.

[Kryvich 163]

@Ugochukwu Mmaduekwe Delphi can convert a string to PChar, and PChar to TCharArray.

[Cristian Peța 94]

1 hour ago, Ugochukwu Mmaduekwe said:

Thanks but am trying to avoid the string helper functions, I also want to avoid using *move* on strings because I heard some time back that it breaks reference counting on strings.

It can brake reference counting only if you move() to string.

When you only move() from string the string is not affected in any way. Move() doesn't change the source.

[Ugochukwu Mmaduekwe 42]

14 minutes ago, Cristian Peța said:

It can brake reference counting only if you move() to string.

When you only move() from string the string is not affected in any way. Move() doesn't change the source.

Thanks a lot for the explanation.

Edited November 21, 2018 by Ugochukwu Mmaduekwe