From 8624761690912169840 X-Google-Thread: f78e5,f6130266038a8c4d X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news2.google.com!news.maxwell.syr.edu!newsfeed.vmunix.org!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!stump.algebra.com!devnull From: ben04_01@freenet.de (Ben Strasser) Newsgroups: comp.std.c++ Subject: Re: Private Methodes declared outside of the class Date: Sat, 21 Aug 2004 22:19:52 GMT Lines: 177 Sender: mail2news@demon.net Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: <2opvdhFdeej3U1@uni-berlin.de> References: <2oblfaF8nds3U1@uni-berlin.de> <2oih41Fb5pb5U1@uni-berlin.de> <8b42afac.0408200500.48e13c94@posting.google.com> NNTP-Posting-Host: news.news.demon.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Trace: news.demon.co.uk 1093126797 27663 158.152.254.254 (21 Aug 2004 22:19:57 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Sat, 21 Aug 2004 22:19:57 +0000 (UTC) X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-User-Agent: Mozilla Thunderbird 0.7.3 (Windows/20040803) X-Spam-Checker-Version: SpamAssassin 2.64-mulga_r1 (2004-01-11) on mulga.cs.mu.OZ.AU X-Orig-X-Trace: news.uni-berlin.de iA1zEv7Os3fCP1D25yb3XwMvqQws33KO3Btun19Hu3GqZgyfuo X-Spam-Status: No, hits=-4.2 required=5.0 tests=BAYES_00,FROM_ENDS_IN_NUMS autolearn=no version=2.64-mulga_r1 X-Accept-Language: en-us, en X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id i7LMJqig016179; Sun, 22 Aug 2004 08:19:52 +1000 (EST) X-Path: comp-std-cpp-robomod!not-for-mail X-Spam-Level: X-Delivered-To: std-c++@ucar.edu X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Newsgroups: comp.std.c++ Xref: g2news1.google.com comp.std.c++:1990 James Kuyper wrote: >>>If you could declare member functions outside the class definition, > > anyone could hijack the class (for good or bad purposes), or break the > class invariants without anyone knowing. I explained this already several times (including in the original post) but here goes again. A privat Methode can only be called from a public or protected one. A method that is public or protected is not private and therefor has to be in the class declaration. Here's a bit of code: class A{ int a; }; void A::foo(){ a=4; } int main(){ A a; //a.foo(); error foo is private } >But if it didn't have access to the class's private parts, it wouldn't >really be a member of that class. I never said that you wouldn't have access to a class's private parts. Here is what I suggest: 1)A method can be declared inside a class declaration private, protected or public. Also it may be declared virtual, static or inline. 2)If a method is not declared inside the class but declared (or defined) outside of the class it is automaticaly assumed to be private, non virtual, non static and non inline. 3)The syntax for declaring/defining a method outside of the class is similar to declaring/defining a normal function except that the name of the method is preceded by class_name:: . 4)A friend may access all methods that have been declared when the compiler reaches the definition of the friend. If the friend is a class then it may access all of the methods that have been declared when the compiler reaches the definition of the method. This means the follwing code would work: class A{ int a; public: void do_stuff(); }; void A::foo(); void A::do_stuff(){ foo(); } void A::foo(){ a=5; } and the following: class B; class A{ friend class B; int a; }; class B{ public: void do(A&); } void A::foo(){ a=5; } void B::do(A&a){ a.foo(); } but not the following: class A{ int a; }; void A::foo(){ a=4; } int main(){ A a; //a.foo(); error foo is private } the following is ok but does it do anything?: class A{ int a; }; void A::foo(){ a=4; } int main(){ A a; } There's no public or protected method so foo can not be called. (You can program a hacking functions but you can not execute it.) With this allowed you can minize the changes that are needed to a header when the implementation is changed: //Header class String{ char*str; unsigned alloced_chars; public: String(); ~String(); set_size(unsigned size); }; //Old implementation unit String::String(): str(new char[1]), alloced_chars(1){ str[0]=0; } String::~String(){ delete[] str; } void String::set_size(unsigned size){ delete[]str; alloced_chars=size+1; str=new char[alloced_chars]; str[size]=0; } //New implementation String::String(): str(new char[1000]), alloced_chars(1000){ str[0]=0; } String::~String(){ delete[] str; } unsigned String::get_size(){ unsigned size=0; while(str[size]!=0) ++size; return size; } void String::enlarge(){ unsigned size=get_size(); delete[]str; alloced_chars*=2; str=new char[alloced_chars]; str[size]=0; } void String::set_size(unsigned new_size){ if(alloced_chars<=new_size) enlarge(); else str[new_size]=0; } (I know that that string class doesn't copy the string when enlarging but I want to keep the example small and simple) And the whole thing without changing a single charachter in the whole header. Meaning no other implementation unit will be recompiled because we changed the implementation of the string class. Also the header does not contain more info than is needed. This makes parsing it a bit faster and makes it a bit simpler for the eye to read (less useless junk to ignore). The alternativ would be to put everything into set_size, so that it would do more than just one thing and things would start to get messy. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ]