C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  hash_map creates access violation errors          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Rebecca Hoffmann Guest Posted: Tue Jun 07, 2005 1:14 pm    Post subject: hash_map creates access violation errors hi, I use a hash_map for storing 4x4 DCT-Blocks. Therefore I convert each block into a string looking like: ":-88:-3:-9:-91:-44:1:-7:-93:88:-1:9:42:-2:-2:-6:". Then I use the following code to identify blocks that have been seen before. -- code ------------- std::hash_map<std::string, int> blockMap; //initialize hash_map .... // add blockString to hashmap if (blockMap[blockString] == NULL) { blockMap[blockString] = ++blockIDcounter; blockID = blockIDcounter; } else { blockID = blockMap[blockString]; } -- end of code ------- The blockIDcounter counts the number of different blocks. during calculation of the first image frame, there is always a runtime error (access violation reading/writing to a certain address) when reaching a blockIDcounter around 1800. So, what could be the reason for this problem? I use Visual Studio C++ ..NET 2003. best regards, Rebecca Hoffmann -- [email]rebecca.hoffmann (AT) tut (DOT) fi[/email] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Maeder Guest Posted: Tue Jun 07, 2005 10:49 pm    Post subject: Re: hash_map creates access violation errors [email]Rebecca.Hoffmann (AT) gmail (DOT) com[/email] (Rebecca Hoffmann) writes: Quote: I use a hash_map for storing 4x4 DCT-Blocks. Therefore I convert each block into a string looking like: ":-88:-3:-9:-91:-44:1:-7:-93:88:-1:9:42:-2:-2:-6:". Then I use the following code to identify blocks that have been seen before. -- code ------------- std::hash_map<std::string, int> blockMap; //initialize hash_map ... // add blockString to hashmap if (blockMap[blockString] == NULL) { Why NULL? The value type of blockMap is int, so why don't you write 0? Quote: blockMap[blockString] = ++blockIDcounter; blockID = blockIDcounter; } else { blockID = blockMap[blockString]; } -- end of code ------- The blockIDcounter counts the number of different blocks. during calculation of the first image frame, there is always a runtime error (access violation reading/writing to a certain address) when reaching a blockIDcounter around 1800. Please post the minimal (<50 lines) complete program that produces this access violation so that your audience can see what you are seeing. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Branimir Maksimovic Guest Posted: Thu Jun 09, 2005 3:44 pm    Post subject: Re: hash_map creates access violation errors Rebecca Hoffmann wrote: Quote: hi, -- code ------------- std::hash_map<std::string, int> blockMap; //initialize hash_map ... during calculation of the first image frame, there is always a runtime error (access violation reading/writing to a certain address) when reaching a blockIDcounter around 1800. So, what could be the reason for this problem? I use Visual Studio C++ .NET 2003. First try with std::map, not hash_map. If map works and hash_map don't, then default hash function for string probably doesn't work, so you must provide your own hashing function (read the docs I guess). Greetings, Bane. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Martin Bonner Guest Posted: Fri Jun 10, 2005 4:30 pm    Post subject: Re: hash_map creates access violation errors Branimir Maksimovic wrote: Quote: Rebecca Hoffmann wrote: hi, -- code ------------- std::hash_map<std::string, int> blockMap; //initialize hash_map ... during calculation of the first image frame, there is always a runtime error (access violation reading/writing to a certain address) when reaching a blockIDcounter around 1800. So, what could be the reason for this problem? I use Visual Studio C++ .NET 2003. First try with std::map, not hash_map. If map works and hash_map don't, then default hash function for string probably doesn't work, so you must provide your own hashing function (read the docs I guess). That seems unlikely. If the hash function is poor (eg "hash() { return 0; }" ) then the performance of the hash_map will be appalling, but the behaviour should be the same. It looks to me like there is some memory corruption going on somewhere, or indirection through an invalidated iterator, or something similar. [ 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.