Subject: Re[7]: setup-2.243 Crash / Install from Local Directory / WinXP
From: Pavel Tsekov <[email-masked]>
To: "Robert Collins" <[email-masked]>
Cc: [email-masked]
Date: Thu, 23 May 2002 12:11:24 +0200

Hello Robert,

Thursday, May 23, 2002, 11:47:26 AM, you wrote:

>> Well, this will fix the problem, but String::substr() will
>> still cause a crash if for some reason a NULL pointer is 
>> passed to it! Btw have you read my mail till the end ?

RC> Yes. The String++ implementation currently uses the <string> std class
RC> to implement substr. From a quick inspection the fault is in the
RC> string() constructor not returning an empty string when NULL is passed
RC> to it.

No! The string constructor which uses const char * as its argument - there is
no check if the pointer being passed is NULL and later strlen () is
called on the pointer to determined the size of the C string being
passed... Here is the exact flow:

1. The constructor
 basic_string (const charT* s)
    : dat (nilRep.grab ()) { assign (s); }

2. The assign call
  basic_string& assign (const charT* s)
    { return assign (s, traits::length (s)); }

3. The call to traits::length()
  static size_t length (const char_type* s)     { return strlen (s); }

The crash happens in 3 - a string object is never constructed at all
and string::substr() is never called. This is a bug of the string
implementation  in 2.95.3. I'am aware of this because I've done alot of
usage of strings lately and was bit by this. I avoid this by calling
string::assign () instead of the string (const char *) constructor
which is safe.

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