Snap7.cpp - CliErrorText - Wrong TextLen

[Keith Birkenkampf]

Dear Snap7 Community and Developer,
i use ur library for a studentproject. I found a small bug in your Code.
In snap7.cpp you have this code:

TextString CliErrorText(int Error)
{
    char text[TextLen];
    Cli_ErrorText(Error, text, TextLen);
    return TextString(text);
}

and in snap7_libmain.cpp you have the following code:

int S7API Cli_ErrorText(int Error, char *Text, int TextLen)
{
    try{
        ErrCliText(Error, Text, TextLen);
        Text[TextLen] = '\0';
    }
    catch (...){
        return errLibInvalidParam;
    }
    return 0;
}

Here you write the '\0' at the position TextLen and that is after the char[] and not within. I think it should be [TextLen - 1].
With the original code i get some: STATUS_STACK_BUFFER_OVERRUN. (Qt Creator)

I use the Snap7 1.4.2 Version from Sourceforge.

I hope i could help you!

[Davide Nardella]

Many thanks ;) , I will look at it.

I looked, you are right.
I will fix it into next release.

[RBob]

Hi Davide, thank you very much for Snap7 library!

I probably found a similar error.
I'm using Snap7.pas (1.4.2) in DelphiXE4 and CliErrorText funtion return me an empty string.
So, to test it, I simulate an error and I debug your CliErrorText to indagate the problem;
with a breakpoint on the last line of the code, Result seems to be correct, but it becomes empty returning the value in the caller. Probably there is a problem in the strings transformation: it seems an error in the pascal string length assignement (or the error is in the external function CliErrorText as Keith suggested).

This is your code:

function CliErrorText(Error : integer) : string;
Var
Text : packed array[0..TextLen-1] of AnsiChar;
begin
if Cli_ErrorText(Error, @Text, TextLen)=0 then
Result:=String(Text)
else
Result:='LIB : Error getting text';
end;

Follow versions seem to solve the problem:

function CliErrorText(Error: Integer): string;
const TextLen = 1024;
var Text: PAnsiChar;
begin
GetMem(Text, TextLen * SizeOf(AnsiChar));
try
if Cli_ErrorText(Error, Text, TextLen)=0 then
Result:= string(Text)
else Result:='LIB : Error getting text';
finally
FreeMem(Text);
end
end;

{// versione alternativa
function CliErrorText(Error : integer) : string;
const TextLen = 1024;
var Text : packed array[0..TextLen-1] of AnsiChar;
Len: Integer;
begin
if Cli_ErrorText(Error, @Text, TextLen)=0 then begin
Result:= Text;
Len:= 0; while Text[Len]<>#0 do Inc(Len);
SetLength(Result, Len)
end else
Result:='LIB : Error getting text';
end;}

Thank you!

[Davide Nardella]

thanks for reporting.
I fixed the error reported by Keith, try to re-download Snap7 1.4.2. I use Snap7 mainly with Delphi (XE5) and works fine.

[RBob]

ok, thank you;
last download works perfectly!
r.