BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  String to Char, how?          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Usage) View previous topic :: View next topic   Author Message b Guest Posted: Wed Jul 30, 2003 1:31 pm    Post subject: String to Char, how? if i have a String ciao = "Hey guys"; char bye[20]; now i want put ciao in bye, how? how can, futhermore, understand the lenght of ciao? At this lenght i must add another caracter for '' character or it is just inserted? Back to top Remy Lebeau (TeamB) Guest Posted: Wed Jul 30, 2003 4:55 pm    Post subject: Re: String to Char, how? "Jonathan Arnold" <jdarnold (AT) buddydog (DOT) org> wrote Quote: strcpy( bye, ciao.c_str() ); That is very dangerous. You should never use strcpy(). Use strncpy() instead. Using strcpy(), if ciao ever happens to be larger than 20 characters, you will overrun your bye buffer and your program will have undefined behavior from that time onwards as you have now modified the memory located after the bye buffer. Quote: using the Length() method. A better way of copying the string: char* bye = new char[ciao.Length()+1]; strcpy( bye, ciao.c_str() ); That, on the other hand, is safer for using strcpy() with. Although you have to be careful now about the 'new' failing if the memory cannot be allocated, particularly if ciao is large. Also do not forget to free bye when you are done with it: delete[] bye; Gambit Back to top Duane Hebert Guest Posted: Thu Jul 31, 2003 12:17 pm    Post subject: Re: String to Char, how? Quote: So strncpy isn't any better if you don't know the sizes somehow. But you do know the size whenever using strncpy(), that is the primary reason people choose to use it in the first place. And if they don't know the size, then they can't call strncpy() in the first place anyway, so they re-write their code so that they will know the size when needed. The thing about strncpy is that you may end up with an unterminated string. If the source string is longer than the target, strncpy will copy n characters to the target but will not append the ''. You would need to create a target char array big enough to hold the source + a null in either case and with strncpy make sure to append the null. I assume this is all because some part of ciao needs to be passed to a function requiring a char*. Why not just substring it to another String or string and pass it with the c_str()? Back to top Yahia El-Qasem Guest Posted: Thu Jul 31, 2003 12:22 pm    Post subject: Re: String to Char, how? Why not do the following : AnsiString X = "blabla..."; char *bye = NULL; bye = new char [ X.Length () + 1 ]; if ( bye ) { memset ( bye, 0x00, X.Length () + 1 ); strncpy ( bye, X.c_str(), X.Length () ); // not X.Length () + 1 because this way my 0x00 at the is still there whatever happens while copying... } This way "bye" is always under any circumstances terminated and there will never be any sort of buffer overrun whatsoever... Just my 2 cents... Yahia Back to top Remy Lebeau (TeamB) Guest Posted: Thu Jul 31, 2003 4:54 pm    Post subject: Re: String to Char, how? "Duane Hebert" <spoo (AT) flarn (DOT) com> wrote Quote: The thing about strncpy is that you may end up with an unterminated string. Yes, if the end of the destination buffer is reached before the null terminator is encountered. Which is why your buffers should always be declared to contain extra room for the null terminator. When calling strncpy(), pass it a length value that is at least 1 character less than the overall size of the destination buffer, and make sure that the extra room is intialized ot set to '' before the buffer is used after the copying. Quote: I assume this is all because some part of ciao needs to be passed to a function requiring a char*. Why not just substring it to another String or string and pass it with the c_str()? That is only when passing the AnsiString to functions taking char* parameters, or for otherwise other reasons where accessing the raw data of the AnsiString is desired. But there are certainly other cases where copying the AnsiString into a char[] array/buffer is desired instead. One possibility is when copying the AnsiString into a structure that declared fixed-sized buffers for any strings it contains. That is one common practice in development your own custom API, especially when DLLs are concerned, for example. Gambit Back to top Jonathan Arnold Guest Posted: Thu Jul 31, 2003 6:18 pm    Post subject: Re: String to Char, how? Remy Lebeau (TeamB) wrote: Quote: "Jonathan Arnold" <jdarnold (AT) buddydog (DOT) org> wrote in message news:3f282507$1 (AT) newsgroups (DOT) borland.com... Well, yes, that's true, but using strncpy isn't going to help you all that much either if you aren't careful there. It is a lot safer than using strcpy() though, as strcpy() copies an arbitrary amount of data from the source until a null terminator is encountered. It does no validation of either the source buffer size of the destination buffer size at all, or even that the memory being copied from is valid. Whereas strncpy() forces you to specify the actual size of the I guess we'll just have to agree to disagree then. I don't see strncpy as being any more inherently safer than strcpy. Neither does any sort of size validation, and both require you to know in some way the size of the destination. And strncpy adds in all the extra stuff about adding in the terminating '', which is just as likely, in my mind, to get forgotten as overwriting it. Mind you, I'm not saying that strcpy is safe. I'm saying that both strcpy and strncpy are inherently dangerous things to use, and there is almost no excuse in this day and age to use either. -- Jonathan Arnold C/C++/CBuilder Keen Advice: http://www.keen.com/categories/categorylist_expand.asp?sid=5156620 Comprehensive C++Builder link site: http://www.buddydog.org/C++Builder/c++builder.html Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         BorlandTalk.com Forum Index -> C++ Builder (VCL Components Usage) All times are GMT Page 1 of 1   Jump to: Select a forum C++ Builder Newsgroups----------------C++ BuilderC++ Builder (ActiveX)C++ Builder (Announcements)C++ Builder (Command Line Tools)C++ Builder DatabasesC++ Builder Databases (ADO)C++ Builder Databases (Desktop)C++ Builder Databases (InterBase Express)C++ Builder Databases (Multi-Tier)C++ Builder Databases (SQL Servers)C++ Builder (Graphics)C++ Builder (IDE)C++ Builder (Internet)C++ Builder (Internet Socket)C++ Builder (Internet Web)C++ Builder (Jobs)C++ Builder (Language)C++ Builder (Language C++)C++ Builder (Compatibility with MFC)C++ Builder (Native API)C++ Builder (Non-Technical)C++ Builder (Students)C++ Builder (Third Party Tools)C++ Builder (Upgrade)C++ Builder (VCL)C++ Builder (VCL Components Usage)C++ Builder (VCL Components Development)C++ Builder (VCL Usage)C++ Builder (WinAPI)C++ Builder Installation Delphi Newsgroups----------------Delphi (General)Delphi ActiveX Controls UsageDelphi ActiveX Controls DevelopmentDelphi As400Delphi DatabasesDelphi Databases (ADO)Delphi Databases (dbExpress)Delphi Databases (Desktop)Delphi Databases (InterBase Express)Delphi Databases (Multi-Tier)Delphi Databases (SQL Servers)Delphi DeploymentDelphi GraphicsDelphi IDEDelphi InternationalizationDelphi InternetDelphi Internet Isapi-WebBrokerDelphi Internet WebSnapDelphi Internet WinsockDelphi JobsDelphi Language BASMDelphi Language ObjectPascalDelphi Model Driven Architecture (General)Delphi Model Driven Architecture (Third Party)Delphi MultimediaDelphi Native APIDelphi Non-TechnicalDelphi ObjectPascalDelphi OLE AutomationDelphi OO designDelphi OpenToolsAPIDelphi Reporting-ChartingDelphi RTLDelphi StudentsDelphi TeamSourceDelphi Thirdparty ToolsDelphi Thirdparty Tools (General)Delphi Thirdparty Tools (IntraWeb)Delphi Thirdparty Tools (RaveReports)Delphi UpgradeDelphi VCLDelphi VCL ComponentsDelphi VCL Components UsingDelphi VCL Components WritingDelphi WebServices SOAPDelphi WinAPIDelphi XMLDelphi Installationcomp.lang.pascal.delphi.components.misccomp.lang.pascal.delphi.components.usagecomp.lang.pascal.delphi.components.writingcomp.lang.pascal.delphi.databasescomp.lang.pascal.delphi.misccomp.sources.delphi JBuilder Newsgroups----------------JBuilderJBuilder AnnouncementsJBuilder Applet IssuesJBuilder As400JBuilder CompilerJBuilder CORBA/RMIJBuilder DatabasesJBuilder DB SwingJBuilder DebuggerJBuilder DeploymentJBuilder DocumentationJBuilder EnterpriseJBuilder HandheldJBuilder IDEJBuilder JavaJBuilder JavaAPIJBuilder Java LanguageJBuilder Java SwingJBuilder Java BeansJBuilder Java Beans UsageJBuilder Java Beans DevelopmentJBuilder JBCLJBuilder JDataStoreJBuilder JobsJBuilder LinuxJBuilder MacintoshJBuilder & MobileSetJBuilder MultiLingual AppsJBuilder Non-TechnicalJBuilder OpenToolsJBuilder Servlets (JSP)JBuilder StudentsJBuilder Team DevelopmentJBuilder Thirdparty ToolsJBuilder UpgradeJBuilder Installation InterBase Newsgroups----------------InterBaseInterBase Bug DiscussionInterBase GeneralInterBase IBConsoleInterBase OpenSourceInterBase ReplicationInterBase SQLInterBase ThirdpartyInterBase Installation Miscellaneous Borland Newsgroups----------------AppCenterAppServerEnteraVisiBroker  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.