C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Elementary question on const          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Last Timer Guest Posted: Sun Jan 30, 2005 7:31 pm    Post subject: Elementary question on const I encountered the following code in Bruce Eckel's online book. Can you please clarify what "const char* const data;" means? Thanks //: C01:MyError.cpp {RunByHand} class MyError { const char* const data; public: MyError(const char* const msg = 0) : data(msg) {} }; void f() { // Here we "throw" an exception object: throw MyError("something bad happened"); } int main() { // As you'll see shortly, we'll want a "try block" here: f(); } ///:~ Back to top Mike Wahler Guest Posted: Sun Jan 30, 2005 7:51 pm    Post subject: Re: Elementary question on const "Last Timer" <dakshing64 (AT) yahoo (DOT) com> wrote Quote: I encountered the following code in Bruce Eckel's online book. Can you please clarify what "const char* const data;" means? Doesn't the book explain it? Quote: //: C01:MyError.cpp {RunByHand} class MyError { const char* const data; This means that the data member 'data' is a const pointer to a const type 'char' object. I.e. neither the pointer nor what it points to may be modified. (If you try, your compiler should complain). -Mike Back to top David Harmon Guest Posted: Sun Jan 30, 2005 8:06 pm    Post subject: Re: Elementary question on const On 30 Jan 2005 11:31:14 -0800 in comp.lang.c++, "Last Timer" <dakshing64 (AT) yahoo (DOT) com> wrote, Quote: please clarify what "const char* const data;" means? Thanks The first "const" means the characters pointed to cannot be changed via this pointer. The second one means the pointer value cannot be changed. Back to top Thomas Matthews Guest Posted: Sun Jan 30, 2005 8:26 pm    Post subject: Re: Elementary question on const Last Timer wrote: Quote: I encountered the following code in Bruce Eckel's online book. Can you please clarify what "const char* const data;" means? Thanks Pointers have two attributes that can be constant: the content of the pointer and the object {date} it points to. Many people say that reading from right to left is easier. const char * const data; ^ ^-- The pointer is constant. Quote: -- The data is constant. When the pointer is constant, it cannot point to other objects. When the data is constant, the data cannot be modified by dereferencing the pointer. -- Thomas Matthews C++ newsgroup welcome message: http://www.slack.net/~shiva/welcome.txt C++ Faq: http://www.parashift.com/c++-faq-lite C Faq: http://www.eskimo.com/~scs/c-faq/top.html alt.comp.lang.learn.c-c++ faq: http://www.comeaucomputing.com/learn/faq/ Other sites: http://www.josuttis.com -- C++ STL Library book http://www.sgi.com/tech/stl -- Standard Template Library Back to top Last Timer Guest Posted: Sun Jan 30, 2005 8:30 pm    Post subject: Re: Elementary question on const Thanks for your kind replies. Do you read it Left to Right or vice versa to determine "first" and "second"? The C++ for Dummies saz on pg 63 const char * pcc="This is a constant string"; char * const cpc="tjhis is also a string"; *pcc='a'; //illegal *cpc ='b';//legal pcc="another string" ; //legal cpc="another string"; illegal I'm trying to develop a mnemonic to remember these. Instead of rote learning may be someone can help me figure this out logically. Thanks again. Back to top Mike Wahler Guest Posted: Sun Jan 30, 2005 8:54 pm    Post subject: Re: Elementary question on const "Last Timer" <dakshing64 (AT) yahoo (DOT) com> wrote Quote: Thanks for your kind replies. Do you read it Left to Right or vice versa to determine "first" and "second"? The C++ for Dummies saz on pg 63 const char * pcc="This is a constant string"; char * const cpc="tjhis is also a string"; *pcc='a'; //illegal *cpc ='b';//legal pcc="another string" ; //legal cpc="another string"; illegal I'm trying to develop a mnemonic to remember these. Instead of rote learning may be someone can help me figure this out logically. http://www.ericgiguere.com/articles/reading-c-declarations.html Yes, it's about C, but applies to C++ as well. (But of course it won't cover the 'C++-only' stuff such as class members, etc. I don't know of a web link for that, but this one should give you a good start.) Also, google for a utility called 'cdecl', which can take a C declaration and translate it to English. It's available for most platforms, and is supplied with some. -Mike 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.