C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  why char * gets overwritten after some time in execution...          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Jigar Mehta Guest Posted: Fri Jan 28, 2005 6:23 am    Post subject: why char * gets overwritten after some time in execution... Hye all, I have noted while debugging my program (or also in runtime execution) that sometimes (not regularly) char * pointer gets overwritten and looses its value... So, because of this my couple of products have failed and this is the reason I have made it compulsary to use char [] instead of char * because char[] don't overwrite our data... So, anybody from you can please make me understand why this happens ?? suppose my code is, char *name; strcpy(name, "Jigar Mehta"); .. .. .. .. //After some lines of execution (say 50 lines) if I see what's there in name address, it gets overwritten and value becomes "" instead of "Jigar Mehta"... Back to top Gianni Mariani Guest Posted: Fri Jan 28, 2005 6:53 am    Post subject: Re: why char * gets overwritten after some time in execution Jigar Mehta wrote: Quote: Hye all, I have noted while debugging my program (or also in runtime execution) that sometimes (not regularly) char * pointer gets overwritten and looses its value... So, because of this my couple of products have failed and this is the reason I have made it compulsary to use char [] instead of char * because char[] don't overwrite our data... So, anybody from you can please make me understand why this happens ?? suppose my code is, char *name; strcpy(name, "Jigar Mehta"); General answer to your problem - USE std::string. Your problem is that "char *" is a *POINTER* to a char (or the first element in an array of chars). The definition : char * str; Does not allocate any storage for "char"s at all and if you write to an unitialized "str" you are invoking - UNDEFINED BEHAVIOUR. For example: char * str; strcpy(str, "THIS OVERWRITES SOME RANDOM PLACE IN MEMORY"); You can allocate "automatic" storage by placing an array of chars in the function and then point to it however this is another source of "UNDEFINED BEHAVIOUR". e.g. char * foo() { char data[ 100 ]; char * pointer_to_char; pointer_to_char = &data[0]; strcpy(str, "THIS IS DEALLOCATED WHEN EXECUTION LEAVES SCOPE"); return pointer_to_char; } Back to top Jigar Mehta Guest Posted: Fri Jan 28, 2005 7:02 am    Post subject: Re: why char * gets overwritten after some time in execution Thanks for you reply, but I am new to std::string that you suggested.. You please tell me how to use this in program by giving a code... I understand the prob. that char * is doing... and I am programming in MS VC++ 6.0.. So, will I be able to use std::string normally or any special .h should be included.. Thanks again, Jigar Mehta Back to top Karl Heinz Buchegger Guest Posted: Fri Jan 28, 2005 11:23 am    Post subject: Re: why char * gets overwritten after some time in execution Jigar Mehta wrote: Quote: Thanks for you reply, but I am new to std::string that you suggested.. You please tell me how to use this in program by giving a code... I understand the prob. that char * is doing... and I am programming in MS VC++ 6.0.. So, will I be able to use std::string normally or any special .h should be included.. You need a book. Seriously. "Accelerated C++" by "Koenig & Moo" is often a good choice. -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Jigar Mehta Guest Posted: Fri Jan 28, 2005 12:01 pm    Post subject: Re: why char * gets overwritten after some time in execution Thanks for the suggestion.. I will refer to it.. Back to top Ioannis Vranos Guest Posted: Sat Jan 29, 2005 12:59 am    Post subject: Re: why char * gets overwritten after some time in execution Jigar Mehta wrote: Quote: Thanks for you reply, but I am new to std::string that you suggested.. You please tell me how to use this in program by giving a code... I understand the prob. that char * is doing... and I am programming in MS VC++ 6.0.. So, will I be able to use std::string normally or any special .h should be included.. VC++ 6 is too old and does not support the language in a satisfactory level. Use VC++ 7.x (2002, 2003) or you can download and install Dev-C++: http://www.bloodshed.net/dev/devcpp.html -- Ioannis Vranos http://www23.brinkster.com/noicys Back to top Jigar Mehta Guest Posted: Sat Jan 29, 2005 4:16 am    Post subject: Re: why char * gets overwritten after some time in execution OK!! then is Dev-C++ giving same or more functionalities than what vc++ 6.0 provides.. As I am used to get features from VC++ 6.0 so, It would be difficult for me to migrate to something giving lesser functionality... Back to top Jack Klein Guest Posted: Sat Jan 29, 2005 5:30 am    Post subject: Re: why char * gets overwritten after some time in execution On 27 Jan 2005 22:23:04 -0800, "Jigar Mehta" <jigarmehta (AT) gatescorp (DOT) com> wrote in comp.lang.c++: Quote: Hye all, I have noted while debugging my program (or also in runtime execution) that sometimes (not regularly) char * pointer gets overwritten and looses its value... So, because of this my couple of products have failed and this is the reason I have made it compulsary to use char [] instead of char * because char[] don't overwrite our data... If the return address is legitimate, here is a statement from the home page of Jigar Mehta's employer: "GATES Information focuses on software products and software services with international resources and access to latest technologies. With our highly trained development teams; a blend of experience and academic qualifications, quality and timely services are being offered by us." If the OP is member of one of their development teams, with a blend of experience and academic qualifications, and not just a first semester student, I shudder. And I would avoid owning stock in the company... -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html Back to top Jigar Mehta Guest Posted: Sat Jan 29, 2005 5:48 am    Post subject: Re: why char * gets overwritten after some time in execution Thanks for the comment.. Jigar mehta is himself representing for the question.. No need to comment on GATES Information.. and it will take some time to analyse http://JK-Technology.com Thanks again for pointing... Back to top Jigar Mehta Guest Posted: Sat Jan 29, 2005 5:51 am    Post subject: Re: why char * gets overwritten after some time in execution And If I give my introduction to you, I am M.Sc. in computer application and information techology (not a first year student.. but thanks for giving a challenge, i like it).. age is 22.. from India.. Back to top Ioannis Vranos Guest Posted: Sat Jan 29, 2005 8:50 am    Post subject: Re: why char * gets overwritten after some time in execution Jack Klein wrote: Quote: If the return address is legitimate, here is a statement from the home page of Jigar Mehta's employer: "GATES Information focuses on software products and software services with international resources and access to latest technologies. With our highly trained development teams; a blend of experience and academic qualifications, quality and timely services are being offered by us." If the OP is member of one of their development teams, with a blend of experience and academic qualifications, and not just a first semester student, I shudder. And I would avoid owning stock in the company... Well he may program in some other programming language(s) and just checking C++ (or C thinking that it is the same, while it is not). -- Ioannis Vranos http://www23.brinkster.com/noicys Back to top Old Wolf Guest Posted: Sun Jan 30, 2005 8:04 pm    Post subject: Re: why char * gets overwritten after some time in execution Jigar Mehta wrote: Quote: char *name; strcpy(name, "Jigar Mehta"); And If I give my introduction to you, I am M.Sc. in computer application and information techology (not a first year student.. but thanks for giving a challenge, i like it).. age is 22.. from India.. What university? Let us know, so we can avoid taking their C courses (and their English courses, for that matter). Back to top Jigar Mehta Guest Posted: Mon Jan 31, 2005 5:06 am    Post subject: Re: why char * gets overwritten after some time in execution Ha Ha Ha.. Thanks for the complements.. Back to top Shan Guest Posted: Mon Jan 31, 2005 12:14 pm    Post subject: Re: why char * gets overwritten after some time in execution Jigar Mehta wrote: Quote: Ha Ha Ha.. Thanks for the complements.. It is not a complement. Having a Msc degree in Computer Applications doesnt seem to help you in coding correct C++ programs. I know that you have undergone C++ courses in your Msc degree programme. If not then throw the Msc degree out of the window and take some decent course which will teach what it calims to teach you. 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