C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Reference to a reference Goto page 1, 2, 3, 4  Next          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Senthil Guest Posted: Thu Oct 27, 2005 1:10 pm    Post subject: Reference to a reference Hi, I am reading Modern C++ Design where Anderi quoted "C++ does not allow references to references". Assume i have DoThat(const string& strData2) { ... } DoThis(const string& strData) { .. DoThat(strData); } int main() { string Data; DoThis(Data); } Now the strData i have inside DoThis is a reference to Data.The strData2 I have is a reference to strData.i.e strData2 is a reference to a reference. Here Andrei's statement confuses me..Am i missing something? Thanks, Senthil Back to top mlimber Guest Posted: Thu Oct 27, 2005 1:16 pm    Post subject: Re: Reference to a reference Senthil wrote: Quote: Hi, I am reading Modern C++ Design where Anderi quoted "C++ does not allow references to references". Assume i have DoThat(const string& strData2) { ... } DoThis(const string& strData) { .. DoThat(strData); } int main() { string Data; DoThis(Data); } Now the strData i have inside DoThis is a reference to Data.The strData2 I have is a reference to strData.i.e strData2 is a reference to a reference. Here Andrei's statement confuses me..Am i missing something? Thanks, Senthil What's the context (section number and paragraph)? Perhaps he means that you can't do with references what you can do with pointers: int anInt = 42; int *pointer_to_int = &anInt; int **pointer_to_pointer_to_int = &pointer_to_int; Cheers! --M Back to top Dan Cernat Guest Posted: Thu Oct 27, 2005 1:21 pm    Post subject: Re: Reference to a reference Senthil wrote: Quote: Hi, I am reading Modern C++ Design where Anderi quoted "C++ does not allow references to references". Assume i have DoThat(const string& strData2) { ... } DoThis(const string& strData) { .. DoThat(strData); } int main() { string Data; DoThis(Data); } Now the strData i have inside DoThis is a reference to Data.The strData2 I have is a reference to strData.i.e strData2 is a reference to a reference. Here you are wrong. strData2 is a reference to a string according with its declaration. Quote: Here Andrei's statement confuses me..Am i missing something? Thanks, Senthil /dan Back to top makc.the.great@gmail.com Guest Posted: Thu Oct 27, 2005 1:48 pm    Post subject: Re: Reference to a reference mlimber wrote: Quote: you can't do with references what you can do with pointers: int anInt = 42; int *pointer_to_int = &anInt; int **pointer_to_pointer_to_int = &pointer_to_int; than what are references are good for? what can be done with references, that cannot be done with pointers? Back to top Alf P. Steinbach Guest Posted: Thu Oct 27, 2005 1:52 pm    Post subject: Re: Reference to a reference * Senthil: Quote: I am reading Modern C++ Design where Anderi quoted "C++ does not allow references to references". Assume i have DoThat(const string& strData2) { ... } DoThis(const string& strData) { .. DoThat(strData); } int main() { string Data; DoThis(Data); } Now the strData i have inside DoThis is a reference to Data.The strData2 I have is a reference to strData.i.e strData2 is a reference to a reference No, strdata2 refers to the same object that strData refers to. Quote: Here Andrei's statement confuses me..Am i missing something? Yes, in addition to the above, and what Andrei's sentence is all about: that C++ doesn't currently allow the syntax T&&, or U& when U is a reference type, which is the probem for template code (it can be solved, as Andrei shows, but it's awkward). Bjarne Stroustrup has suggested (possibly this was just with regard to template code) that T&& should be allowed, and defined to mean T&. -- A: Because it messes up the order in which people normally read text. Q: Why is it such a bad thing? A: Top-posting. Q: What is the most annoying thing on usenet and in e-mail? Back to top Rolf Magnus Guest Posted: Thu Oct 27, 2005 1:52 pm    Post subject: Re: Reference to a reference Senthil wrote: Quote: Hi, I am reading Modern C++ Design where Anderi quoted "C++ does not allow references to references". Assume i have DoThat(const string& strData2) According to the declaration, strData2 is a reference to const string. Quote: { ... } DoThis(const string& strData) According to the declaration, strData is a reference to const string. Quote: { .. DoThat(strData); } int main() { string Data; DoThis(Data); } Now the strData i have inside DoThis is a reference to Data.The strData2 I have is a reference to strData. It's a refernce to Data. Quote: i.e strData2 is a reference to a reference. No. If allowed, a reference to a reference would be declared something like: const string&& strData2 Back to top deane_gavin@hotmail.com Guest Posted: Thu Oct 27, 2005 1:52 pm    Post subject: Re: Reference to a reference makc.the.gr... (AT) gmail (DOT) com wrote: Quote: mlimber wrote: you can't do with references what you can do with pointers: int anInt = 42; int *pointer_to_int = &anInt; int **pointer_to_pointer_to_int = &pointer_to_int; than what are references are good for? what can be done with references, that cannot be done with pointers? http://www.parashift.com/c++-faq-lite/references.html particularly http://www.parashift.com/c++-faq-lite/references.html#faq-8.6 Gavin Deane Back to top makc.the.great@gmail.com Guest Posted: Thu Oct 27, 2005 2:12 pm    Post subject: Re: Reference to a reference Quote: particularly http://www.parashift.com/c++-faq-lite/references.html#faq-8.6 so, what's your point? what can be done with reference and can not be done with pointer, again? Back to top Senthil Guest Posted: Thu Oct 27, 2005 2:13 pm    Post subject: Re: Reference to a reference Thanks for all your replies..Just to make clear that i've understood it properly, The following should be invalid program right ? int main() { int i = 10; int &r1 = i; int &r2 = r1; return 0; } Best Regards, Senthil Back to top mlimber Guest Posted: Thu Oct 27, 2005 2:15 pm    Post subject: Re: Reference to a reference [email]deane_gavin (AT) hotmail (DOT) com[/email] wrote: Quote: makc.the.gr... (AT) gmail (DOT) com wrote: mlimber wrote: you can't do with references what you can do with pointers: int anInt = 42; int *pointer_to_int = &anInt; int **pointer_to_pointer_to_int = &pointer_to_int; than what are references are good for? what can be done with references, that cannot be done with pointers? http://www.parashift.com/c++-faq-lite/references.html particularly http://www.parashift.com/c++-faq-lite/references.html#faq-8.6 Also, references are necessary for operator overloading: #include <ostream> using namespace std; class Foo { /* ... */ }; ostream& operator<< ( ostream& os, const Foo& foo ) { // Stream elements of Foo here ... return os; } void Bar( const Foo& foo ) { cout << "Here's your Foo:n" << foo << endl; // ... } We couldn't do this with pointers. Cheers! --M Back to top Christian Meier Guest Posted: Thu Oct 27, 2005 2:17 pm    Post subject: Re: Reference to a reference <makc.the.great (AT) gmail (DOT) com> schrieb im Newsbeitrag news:1130422344.258473.298980 (AT) g47g2000cwa (DOT) googlegroups.com... Quote: particularly http://www.parashift.com/c++-faq-lite/references.html#faq-8.6 so, what's your point? what can be done with reference and can not be done with pointer, again? Nothing. AFAIK references are usually implemented as pointers. But references exist because they are more convenient to use because references can't be NULL. Greetings Chris Back to top mlimber Guest Posted: Thu Oct 27, 2005 2:18 pm    Post subject: Re: Reference to a reference Senthil wrote: Quote: Thanks for all your replies..Just to make clear that i've understood it properly, The following should be invalid program right ? int main() { int i = 10; int &r1 = i; int &r2 = r1; return 0; } Best Regards, Senthil No. That is valid. Both r1 and r2 refer to the same object (in this case, i). Cheers! --M Back to top Christian Meier Guest Posted: Thu Oct 27, 2005 2:20 pm    Post subject: Re: Reference to a reference "Senthil" <s.senthilvel (AT) gmail (DOT) com> schrieb im Newsbeitrag news:1130422385.054927.50140 (AT) g14g2000cwa (DOT) googlegroups.com... Quote: Thanks for all your replies..Just to make clear that i've understood it properly, The following should be invalid program right ? int main() { int i = 10; int &r1 = i; int &r2 = r1; return 0; } Best Regards, Senthil No, this program is valid. r2 is a reference to an int as you can see in your declaration of r2: Quote: int &r2 = r1; But as already mentioned before, you can't do something like int&& r2 = r1; Greetings Chris Back to top makc.the.great@gmail.com Guest Posted: Thu Oct 27, 2005 2:26 pm    Post subject: Re: Reference to a reference mlimber wrote: Quote: references are necessary for operator overloading: We couldn't do this with pointers. okay, agreed... though this is because of the way operators are "implemented" or "defined" in c++. I can imagine a language, where there would be no difference between "variables" and "pointers" presented to programmer, so that constants would be only objects.... Back to top deane_gavin@hotmail.com Guest Posted: Thu Oct 27, 2005 2:30 pm    Post subject: Re: Reference to a reference [email]makc.the.great (AT) gmail (DOT) com[/email] wrote: Quote: particularly http://www.parashift.com/c++-faq-lite/references.html#faq-8.6 so, what's your point? what can be done with reference and can not be done with pointer, again? You've snipped a lot of context. You originally asked two questions. 1 what are references are good for? 2 what can be done with references, that cannot be done with pointers? faq 8.6 answers question 1. I also pointed you at all of section 8 http://www.parashift.com/c++-faq-lite/references.html Read this whole section and you will find the answer to question 2 (e.g faq 8.3). HTH Gavin Deane 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 Goto page 1, 2, 3, 4  Next Page 1 of 4   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.