STL Vector - pass by reference?
in [Visual C]
|
Prev: _CrtIsValidHeapPointer Assertion in C++/CLI Application Debug mode.
Next: Error LNK2028 unresolved token / LNK2019 Unrevolved external symbol
From: Ulrich Eckhardt on 13 Aug 2007 08:52 Gerry Hickman wrote: >>> void PopulateStrings(vector<string> * guids) >>> { >>> guids->clear(); >>> guids->push_back("test1"); >>> guids->push_back("test2"); >>> } >> >> While this code will work, there is one thing I object to: in C++, where >> you have references, a pointer[1] means to me that something is optional, >> i.e. passing zero is okay, but you don't mean that. Still, you must >> handle that case, so either you just return (making it a non-error), >> throw an exception (making it a runtime error) or use assert() (making it >> a programmer's error). > > Does this only apply to the 'pointer' version, or does it apply to the > 'references' version too? A reference can't be null, so this doesn't apply. Uli
From: David Wilkinson on 13 Aug 2007 08:56 Gerry Hickman wrote: > I guessed 'returns' should be a comment, but the first two lines didn't > make sense with void following vector<string>::size_type, I guess I was > supposed to _replace_ void with vector<string>::size_type, seems obvious > now. > Does this only apply to the 'pointer' version, or does it apply to the > 'references' version too? Gerry: The "void" is Doug's post was a typo, I think. This confused me also. When you pass a pointer, the "implication" is that it could be NULL, and that the function will take some special action in this case. If you pass a reference, it cannot be NULL (every reference must be initialized to some object), so no such action need be taken. Generally, in C++ references are preferred to pointers. -- David Wilkinson Visual C++ MVP
From: Ben Voigt [C++ MVP] on 13 Aug 2007 09:36 "Ulrich Eckhardt" <eckhardt(a)satorlaser.com> wrote in message news:tp06p4-ile.ln1(a)satorlaser.homedns.org... > Gerry Hickman wrote: >>>> void PopulateStrings(vector<string> * guids) >>>> { >>>> guids->clear(); >>>> guids->push_back("test1"); >>>> guids->push_back("test2"); >>>> } >>> >>> While this code will work, there is one thing I object to: in C++, where >>> you have references, a pointer[1] means to me that something is >>> optional, >>> i.e. passing zero is okay, but you don't mean that. Still, you must >>> handle that case, so either you just return (making it a non-error), >>> throw an exception (making it a runtime error) or use assert() (making >>> it >>> a programmer's error). >> >> Does this only apply to the 'pointer' version, or does it apply to the >> 'references' version too? > > A reference can't be null, so this doesn't apply. That's not true. It's illegal to use a null reference, but in the same way that it's illegal to use a null pointer.
From: Ben Voigt [C++ MVP] on 13 Aug 2007 09:38 "David Wilkinson" <no-reply(a)effisols.com> wrote in message news:eR1GUla3HHA.4584(a)TK2MSFTNGP03.phx.gbl... > Gerry Hickman wrote: >> I guessed 'returns' should be a comment, but the first two lines didn't >> make sense with void following vector<string>::size_type, I guess I was >> supposed to _replace_ void with vector<string>::size_type, seems obvious >> now. > >> Does this only apply to the 'pointer' version, or does it apply to the >> 'references' version too? > > Gerry: > > The "void" is Doug's post was a typo, I think. This confused me also. > > When you pass a pointer, the "implication" is that it could be NULL, and > that the function will take some special action in this case. If you pass > a reference, it cannot be NULL (every reference must be initialized to > some object), so no such action need be taken. This "every reference must be initialized to some object" is not true. Any pointer can be converted to a reference. > > Generally, in C++ references are preferred to pointers. > > -- > David Wilkinson > Visual C++ MVP
From: Bo Persson on 13 Aug 2007 11:26
Ben Voigt [C++ MVP] wrote: :: "Ulrich Eckhardt" <eckhardt(a)satorlaser.com> wrote in message :: news:tp06p4-ile.ln1(a)satorlaser.homedns.org... ::: Gerry Hickman wrote: :::::: void PopulateStrings(vector<string> * guids) :::::: { :::::: guids->clear(); :::::: guids->push_back("test1"); :::::: guids->push_back("test2"); :::::: } ::::: ::::: While this code will work, there is one thing I object to: in ::::: C++, where you have references, a pointer[1] means to me that ::::: something is optional, ::::: i.e. passing zero is okay, but you don't mean that. Still, you ::::: must handle that case, so either you just return (making it a ::::: non-error), throw an exception (making it a runtime error) or ::::: use assert() (making it ::::: a programmer's error). :::: :::: Does this only apply to the 'pointer' version, or does it apply :::: to the 'references' version too? ::: ::: A reference can't be null, so this doesn't apply. :: :: That's not true. It's illegal to use a null reference, but in the :: same way that it's illegal to use a null pointer. There aren't any null references, only invalid ones. Like a reference to an object that has been destroyed. If someone passes an invalid reference to my functions, that is a bug in their code, not my problem. If someone passes a null pointer, I must handle that. Bo Persson |