C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Simple C++ ifstream question          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message AC Slater Guest Posted: Sat Jan 24, 2004 3:10 pm    Post subject: Simple C++ ifstream question In regards to the following code: char tmp[6]; myifstread.read(tmp,5); Does tmp[5] = '' by definition? E.g. does .read put the null terminator? If not, why would it be that for months the print statement after the read would show just 5 characters than out of nowhere sometimes it shows 5 chars and then some garbage? Just trying to understand whats going on here. Frank [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jeff Schwab Guest Posted: Sun Jan 25, 2004 1:33 am    Post subject: Re: Simple C++ ifstream question AC Slater wrote: Quote: In regards to the following code: char tmp[6]; myifstread.read(tmp,5); Does tmp[5] = '' by definition? E.g. does .read put the null terminator? Of course not. What if your buffer were only 5 characters long? Quote: If not, why would it be that for months the print statement after the read would show just 5 characters than out of nowhere sometimes it shows 5 chars and then some garbage? You were unlucky. The array of characters may have started with '' values. Quote: Just trying to understand whats going on here. Frank If you want the old behavior back, initialize the array explicitly. char tmp[ 6 ] = { '' }; [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jonathan Turkanis Guest Posted: Sun Jan 25, 2004 1:35 am    Post subject: Re: Simple C++ ifstream question "AC Slater" <notme (AT) yahoo (DOT) com> wrote Quote: In regards to the following code: char tmp[6]; myifstread.read(tmp,5); Does tmp[5] = '' by definition? E.g. does .read put the null terminator? There would be no reason to insert a null character at index 5. Often when one invokes read one does not read an entire string, but just part of a string or pure binary data. Furthermore, there is no way for the stream to know how large the character buffer actually is. For all it knows, it could have been called in this context: char tmp[5]; myifstread.read(tmp,5); Here, adding a terminating null character would result in underfined behavior. Quote: If not, why would it be that for months the print statement after the read would show just 5 characters than out of nowhere sometimes it shows 5 chars and then some garbage? This behavior is perfectly consistent with the standard. Why it happens I can't say for sure, but it may be that you are sometimes using a static array, which is zero-initialized, or that your implementation zero-initializes arrays in debug mode. Jonathan [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top John Potter Guest Posted: Sun Jan 25, 2004 10:44 am    Post subject: Re: Simple C++ ifstream question On 24 Jan 2004 10:10:08 -0500, AC Slater <notme (AT) yahoo (DOT) com> wrote: Quote: In regards to the following code: char tmp[6]; myifstread.read(tmp,5); Does tmp[5] = '' by definition? No. The read stores exactly the number of characters that you direct. Tmp[5] has whatever garbage was there before the call of read. Quote: E.g. does .read put the null terminator? Absolutely not. Think about int x; myifstream.read((char*)&x, sizeof(x)); Read is an unformatted function. Quote: If not, why would it be that for months the print statement after the read would show just 5 characters than out of nowhere sometimes it shows 5 chars and then some garbage? You were unlucky enough to have some random zeores in memory. It usually works that way until you demo for your most important customer. John [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ Language (Moderated) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.