Caolán McNamara caolanm at redhat.com
Sun Nov 14 13:27:53 PST 2010

Michael mentioned to me that he had seen cases where
"RTL_CONSTASCII_STRINGPARAM" was accidentally used instead of
"RTL_CONSTASCII_USTRINGPARAM". Here's the problem...

#define RTL_CONSTASCII_STRINGPARAM( constAsciiStr ) constAsciiStr,

which turns into two

#define RTL_CONSTASCII_USTRINGPARAM( constAsciiStr ) constAsciiStr,
((sal_Int32)(sizeof(constAsciiStr)-1)), RTL_TEXTENCODING_ASCII_US

which turns into three arguments, the third one being the encoding.

The problem arises when someone is using the old "String" class because
it has a load of constructors, two of which are...

UniString( const sal_Char* pByteStr, rtl_TextEncoding eTextEncoding,


UniString( const sal_Char* pByteStr, xub_StrLen nLen, rtl_TextEncoding
eTextEncoding, sal_uInt32 nCvtFlags =

So if someone uses RTL_CONSTASCII_USTRINGPARAM the right thing happens
and the better fitting second ctor is selected, char*, len, encoding all
filled in correctly.

On the other hand if someone uses RTL_CONSTASCII_STRINGPARAM, then the
better fitting first ctor is selected and the *ENCODING* argument is
filled in with the length of the string. Puke.

I should note that none of these errors are new or have been introduced
recently, but have been lurking in the code for quite a while.

Attached is a patch to the class String class which adds a higher
constructor that exactly matches the output of
RTL_CONSTASCII_STRINGPARAM but marks it private, detecting this misuse
at compile time, which should make this impossible to happen again, but
retain any correct uses of the first constructor where a real 16bit
rtl_TextEncoding is used, and not an implicitly downcasted sal_Int32.

I've applied this patch, and fixed a big pile of incorrect code that
falls out of it. What I will have missed is code which is only compiled
for non-Linux platforms, e.g. MacOSX or Windows specific code. So if you
get a compile failure about something being private in the String class
on those platforms the fix is probably trivially changing a STRINGPARAM
to USTRINGPARAM, otherwise let me know and I'll have a look.

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