BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  strncpy/wcsncpy query (BCB6/STLPort) Goto page 1, 2, 3  Next          BorlandTalk.com Forum Index -> C++ Builder (Language C++) View previous topic :: View next topic   Author Message Andrue Cope [TeamB] Guest Posted: Thu Jul 06, 2006 5:14 pm    Post subject: strncpy/wcsncpy query (BCB6/STLPort) I've just found that wcsncpy() calls wcslen() to determine the length of the source string - surely that's unfair? In this particular case I'm using wcsncpy() because the source string is not '\0' terminated. Is this an STLPort bug or expected behaviour? I'd have thought that wcsncpy() had no business calling wcslen(). -- Andrue Cope [TeamB] [Bicester, Uk] http://info.borland.com/newsgroups/guide.html Back to top Darko Miletic Guest Posted: Thu Jul 06, 2006 5:48 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) Andrue Cope [TeamB] wrote: Quote: I've just found that wcsncpy() calls wcslen() to determine the length of the source string - surely that's unfair? In this particular case I'm using wcsncpy() because the source string is not '\0' terminated. Is this an STLPort bug or expected behaviour? I'd have thought that wcsncpy() had no business calling wcslen(). I do not have bcb6 on this machine but if that is the case it is an error. You have two options: 1. Roll your own version of desired function. 2. Switch to MS strsafe functions. Back to top Andrue Cope [TeamB] Guest Posted: Thu Jul 06, 2006 6:15 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) Darko Miletic wrote: Quote: I do not have bcb6 on this machine but if that is the case it is an error. My thinking too. Perhaps STLPort is trying to optimise wcslen into a memcpy() although that seems pretty pointless. Quote: You have two options: 1. Roll your own version of desired function. Yeah - I used memcpy() :) -- Andrue Cope [TeamB] [Bicester, Uk] http://info.borland.com/newsgroups/guide.html Back to top Bob Gonder Guest Posted: Thu Jul 06, 2006 6:18 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) Andrue Cope [TeamB] wrote: Quote: I've just found that wcsncpy() calls wcslen() to determine the length of the source string - surely that's unfair? I would think so too. You could switch to lstrcpynW (And hope MS doesn't do the same thing) Back to top Rudy Velthuis [TeamB] Guest Posted: Thu Jul 06, 2006 9:10 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) At 15:18:46, 06.07.2006, Bob Gonder wrote: Quote: Andrue Cope [TeamB] wrote: I've just found that wcsncpy() calls wcslen() to determine the length of the source string - surely that's unfair? I would think so too. You could switch to lstrcpynW (And hope MS doesn't do the same thing) I'd rather write my own. Then I'd be sure that it did what I expected it to do. -- Rudy Velthuis [TeamB] http://rvelthuis.de/ "Well done is better than well said." -- Benjamin Franklin (1706-1790) Back to top Thomas Maeder [TeamB] Guest Posted: Thu Jul 06, 2006 9:12 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) "Andrue Cope [TeamB]" <no.spam (AT) not (DOT) a.valid.address> writes: Quote: I've just found that wcsncpy() calls wcslen() to determine the length of the source string - surely that's unfair? I'm not really sure, but I tend to disagree. On my Linux box, I get: % man wcsncpy NAME wcsncpy - copy a fixed-size string of wide characters SYNOPSIS #include <wchar.h> wchar_t *wcsncpy(wchar_t *dest, const wchar_t *src, size_t n); DESCRIPTION The wcsncpy function is the wide-character equivalent of the strncpy function. It copies at most n wide characters from the wide-character string pointed to by src, including the terminating L'\0' character, to the array pointed to by dest. Exactly n wide characters are writ- ten at dest. If the length wcslen(src) is smaller than n, the remain- ing wide characters in the array pointed to by dest are filled with L'\0' characters. If the length wcslen(src) is greater or equal to n, the string pointed to by dest will not be L'\0' terminated. The strings may not overlap. The programmer must ensure that there is room for at least n wide characters at dest. RETURN VALUE wcsncpy returns dest. CONFORMING TO ISO/ANSI C, UNIX98 [That's not a normative text, but I don't have a copy of the C standard.] Note that the behavior of wcsncpy is documented in terms of wcslen() applied to src. This only makes sense if applying wcslen() to src has defined behavior. Back to top Alan Bellingham Guest Posted: Thu Jul 06, 2006 9:27 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) maeder (AT) glue (DOT) ch (Thomas Maeder [TeamB]) wrote: Quote: [That's not a normative text, but I don't have a copy of the C standard.] Note that the behavior of wcsncpy is documented in terms of wcslen() applied to src. This only makes sense if applying wcslen() to src has defined behavior. ------------------------------------------------------------------------- 7.24.4.2.2 The wcsncpy function Synopsis 1 #include <wchar.h> wchar_t *wcsncpy(wchar_t * restrict s1, const wchar_t * restrict s2, size_t n); Description 2 The wcsncpy function copies not more than n wide characters (those that follow a null wide character are not copied) from the array pointed to by s2 to the array pointed to by s1. 288) 3 If the array pointed to by s2 is a wide string that is shorter than n wide characters, null wide characters are appended to the copy in the array pointed to by s1, until n wide characters in all have been written. Returns 4 The wcsncpy function returns the value of s1. .... 288) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the result will not be null-terminated. ------------------------------------------------------------------------- No mention there whatever of the wcslen() requirement. (This is the C99 version.) Alan Bellingham -- Me <url:mailto:alanb (AT) episys (DOT) com> <url:http://www.doughnut.demon.co.uk/> ACCU - C, C++ and Java programming <url:http://accu.org/> The 2006 Discworld Convention <url:http://www.dwcon.org/> Back to top Andrue Cope [TeamB] Guest Posted: Thu Jul 06, 2006 9:31 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) Thomas Maeder [TeamB] wrote: Quote: Note that the behavior of wcsncpy is documented in terms of wcslen() applied to src. This only makes sense if applying wcslen() to src has defined behavior. Interesting. So should the following code be fine or asking for trouble? wchar_t buffer1[ 3 ]; wchar_t buffer2[ 2 ]; buffer2[ 0 ]=L'H'; buffer2[ 1 ]=L'I'; wcsncpy( buffer, buffer2, 2 ); ISTM that it should be fine but if wcsncpy() is using wcslen() it will obviously be undefined. Using wcslen() inside wcsncpy() seems to be causing trouble for no good reason :-/ -- Andrue Cope [TeamB] [Bicester, Uk] http://info.borland.com/newsgroups/guide.html Back to top Thomas Maeder [TeamB] Guest Posted: Fri Jul 07, 2006 2:05 am    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) "Andrue Cope [TeamB]" <no.spam (AT) not (DOT) a.valid.address> writes: Quote: Note that the behavior of wcsncpy is documented in terms of wcslen() applied to src. This only makes sense if applying wcslen() to src has defined behavior. Interesting. But wrong, it seems after Alan's post. Back to top Andrue Cope [TeamB] Guest Posted: Fri Jul 07, 2006 8:10 am    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) Alan Bellingham wrote: Quote: No mention there whatever of the wcslen() requirement. (This is the C99 version.) That's certainly what I'd expect. Making use of wcslen() just limits the usefulness. By its nature the function has to walk the source string looking for a terminator so the only advantage (if it is one) is that it can use a memory copy to transfer the data. -- Andrue Cope [TeamB] [Bicester, Uk] http://info.borland.com/newsgroups/guide.html Back to top Roddy Pratt Guest Posted: Fri Jul 07, 2006 2:03 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) FWIW, the BDS2006 dinkumware library doesn't use wcslen. However, the version of wcsncpy in "\source\cpprtl\source\cstrings" still does! I don't know exactly which gets used and when - is dinkumware not used for console applications?? - Roddy Back to top Andrue Cope [TeamB] Guest Posted: Fri Jul 07, 2006 3:27 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) Roddy Pratt wrote: Quote: However, the version of wcsncpy in "\source\cpprtl\source\cstrings" still does! Yeah :-/ As I suspected it looks like an optimisation. Quote: I don't know exactly which gets used and when - is dinkumware not used for console applications?? I thought it was used all the time with BDS but now I'm not so sure. -- Andrue Cope [TeamB] [Bicester, Uk] http://info.borland.com/newsgroups/guide.html Back to top Bob Gonder Guest Posted: Sat Jul 08, 2006 9:18 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) Rudy Velthuis [TeamB] wrote: Quote: I'd rather write my own. Then I'd be sure that it did what I expected it to do. Kinda defeats the purpose of standard libraries, doesn't it? Back to top Rudy Velthuis [TeamB] Guest Posted: Sat Jul 08, 2006 11:45 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) At 18:18:33, 08.07.2006, Bob Gonder wrote: Quote: Rudy Velthuis [TeamB] wrote: I'd rather write my own. Then I'd be sure that it did what I expected it to do. Kinda defeats the purpose of standard libraries, doesn't it? Sure. But if you can't trust a library, what to do? I personally don't think that wcslen() should have been used. -- Rudy Velthuis [TeamB] http://rvelthuis.de/ "The Stones, I love the Stones. I watch them whenever I can. Fred, Barney..." -- Steven Wright. Back to top Rudy Velthuis [TeamB] Guest Posted: Mon Jul 10, 2006 10:08 pm    Post subject: Re: strncpy/wcsncpy query (BCB6/STLPort) At 14:42:33, 10.07.2006, Hendrik Schober wrote: Quote: Sure. But if you can't trust a library, what to do? [...] Whatever, trading some libraries bugs for your own isn't an option. If you don't even trust your own code, then you are in the wrong business. <g> Especially if this is only a small routine like wcscpy, it is IMO better to use your own code which you fully control, than switch an entire 3rd party library, which may introduce other bugs. -- Rudy Velthuis [TeamB] http://rvelthuis.de/ "I have often regretted my speech, never my silence." - Xenocrates (396-314 B.C.) 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