C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  question about strings          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message wongjoekmeu@yahoo.com Guest Posted: Fri Jan 28, 2005 8:32 am    Post subject: question about strings Hello All, I have the following C++ code which I do not understand. I have a class Employee and a class String. Employee is using data members of type String. The definition of the overloaded constructor of Employee is as follow: ------------- Employee::Employee(char *firstname, char *lastname, char *address, long salary): itsFirstname(firstname), itsLastname(lastname), itsAddress(address), itsSalary(salary) {} ------------- This constructor requires three pointers of type char as input parameter and one long int. So I would suppose that when an object of type Employee is being created that in the input parameters (the first three) should be adresses of objects of type String. But now, to my surprise in the main() function it is written: ------------- Employee Edie("Jane","Doe","1461 Shore Parkway", 20000); ------------- Why is this correct ? The first three input parameters are character strings. How is that possible that this program compiles ?? Somewhere in the comments of the listing it says that the class String know how to convert a character string to a String. But if for instance this is valid and "Jane" is being converted to a String object, but then it is still not a pointer. Can anyone explain this to me. Thank you in advance. Robert Back to top ulrich Guest Posted: Fri Jan 28, 2005 9:00 am    Post subject: Re: question about strings On 28 Jan 2005 00:32:18 -0800, [email]wongjoekmeu (AT) yahoo (DOT) com[/email] <wongjoekmeu (AT) yahoo (DOT) com> wrote: [...] Quote: Employee and a class String. Employee is using data members of type String. [...] Quote: Employee::Employee(char *firstname, char *lastname, char *address, long salary): itsFirstname(firstname), itsLastname(lastname), itsAddress(address), itsSalary(salary) {} [...] Quote: Employee Edie("Jane","Doe","1461 Shore Parkway", 20000); ------------- Why is this correct ? The first three input parameters are character strings. How is that possible that this program compiles ?? Somewhere in the comments of the listing it says that the class String know how to convert a character string to a String. But if for instance this is valid and "Jane" is being converted to a String object, but then it is still not a pointer. Can anyone explain this to me. the string object takes a _copy_ of what your char* is pointing at. that's the whole magic. -- have a nice day ulrich Back to top Ivan Vecerina Guest Posted: Fri Jan 28, 2005 9:19 am    Post subject: Re: question about strings <wongjoekmeu (AT) yahoo (DOT) com> wrote Quote: Hello All, Hi, I have the following C++ code which I do not understand. I have a class Employee and a class String. Employee is using data members of type String. I'll assume you mean std::string ? Quote: The definition of the overloaded constructor of Employee is as follow: ------------- Employee::Employee(char *firstname, char *lastname, char *address, long salary): itsFirstname(firstname), itsLastname(lastname), itsAddress(address), itsSalary(salary) {} ------------- This constructor requires three pointers of type char as input parameter and one long int. So I would suppose that when an object of type Employee is being created that in the input parameters (the first three) should be adresses of objects of type String. But now, to my surprise in the main() function it is written: ------------- Employee Edie("Jane","Doe","1461 Shore Parkway", 20000); ------------- Why is this correct ? std::string (and other string classes) typically have a constructor declared as: std::string::string( char const* p ); This constructor copies the null-terminates string pointed to by p to initialize its contents. Quote: The first three input parameters are character strings. How is that possible that this program compiles ?? Somewhere in the comments of the listing it says that the class String know how to convert a character string to a String. But if for instance this is valid and "Jane" is being converted to a String object, but then it is still not a pointer. Can anyone explain this to me. The data is *copied* by the string constructor into its own storage. Actually, there a different problem with the Employee constructor it describes: its first 3 parameters should not be of type char*, but of either char const* or std::string const&. The declaration: Employee Edie("Jane","Doe","1461 Shore Parkway", 20000); passes string literals ( the "..." stuff ) which normally has type char const* ( actually char const[] ). A deprecated conversion to char* is however available, only for backwards-compatibility with C. I hope this helps, Ivan -- http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form 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 (comp.lang.c++) 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.