C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  trouble understanding a problem when using strcat          C++Talk.NET Forum Index -> C Language View previous topic :: View next topic   Author Message Guest Posted: Mon May 07, 2007 9:11 am    Post subject: trouble understanding a problem when using strcat Perhaps this is obvious but I am not sure what is going on... Here is the relevant code: char *command; char *argument; char url[]="file:///usr/u/myname/Project/cats/"; char target_path[]="/tmp/abc"; command=strtok(buf,":\n\r"); argument=strtok(NULL,"\n\r"); /*now, I want to strcat argument onto both url and target_path */ strcat(url,argument); strcat(target_path,argument); But that doesn't work as I expect it to. Why? What I am seeing is that the first strcat work but the second one has a result string that is all discombobulated somehow? Any advice would be greatly appreciated! Back to top Richard Heathfield Guest Posted: Mon May 07, 2007 9:11 am    Post subject: Re: trouble understanding a problem when using strcat sail0r (AT) creepjoint (DOT) net said: Quote: Perhaps this is obvious but I am not sure what is going on... Here is the relevant code: char *command; char *argument; char url[]="file:///usr/u/myname/Project/cats/"; How much storage is reserved for url[]? Count the bytes in the initialiser to find out. (Add 1 for the terminator.) Call this X. How much of this storage is used? Call this Y. What do you notice about X and Y? [1] Quote: char target_path[]="/tmp/abc"; command=strtok(buf,":\n\r"); argument=strtok(NULL,"\n\r"); /*now, I want to strcat argument onto both url and target_path */ strcat(url,argument); Let us assume that argument now points to a string longer than zero bytes. Z, say, not including the terminator. How much storage will the url[] array require if it is to store both the information it already contains and the Z bytes of information you are now trying to add to it? [2] How much storage does it actually have? [3] How short are you of the necessary bytes? [4] Consider using dynamic memory allocation instead. Answers: [1] They are equal [2] Y + Z [3] Y [4] Z -- Richard Heathfield "Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk email: rjh at the above domain, - www. Back to top Roland Pibinger Guest Posted: Mon May 07, 2007 9:11 am    Post subject: Re: trouble understanding a problem when using strcat On 6 May 2007 22:54:40 -0700, sail0r (AT) creepjoint (DOT) net wrote: Quote: But that doesn't work as I expect it to. Why? Unlike other languages C has no string type. Really. You need to use '\0' terminated char arrays and provide the necessary automatic or dynamic memory space for them. -- Roland Pibinger "The best software is simple, elegant, and full of drama" - Grady Booch 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 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.