- test - 3 Updates
- references in stl - 4 Updates
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Sep 19 08:35PM +0200 my answer in stl/ref thread didn't show up, so, testing (sorry). |
| alf.p.steinbach@gmail.com: Sep 19 11:45AM -0700 On Tuesday, September 19, 2017 at 8:35:53 PM UTC+2, Alf P. Steinbach wrote: > my answer in stl/ref thread didn't show up, so, testing (sorry). Why am I posting to clc++ instead of e.g. no.alt.test? Because the problem is with clc++, when posting from Thunderbird. Again, sorry for the noise. |
| scott@slp53.sl.home (Scott Lurndal): Sep 19 07:54PM >my answer in stl/ref thread didn't show up, so, testing (sorry). propagation delay is inherent in Usenet. |
| porparek@gmail.com: Sep 19 08:56AM -0700 Hi, Could you please explain me why references cannot be stored in STL containers. I found that one of the reasons is that reference cannot be re-initialized. If this is true then why the "T * const" may be stored in STL containers ? Please write me why references cannot be stored in STL containers. thanks for help |
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Sep 19 06:47PM +0200 > Could you please explain me why references cannot be stored in STL containers. They can't be stored DIRECTLY in containers. Most containers, and in particular those in the standard library, don't support reference element type because it would need extra machinery and interface semantics to handle the not-object-ness of references, e.g. that you can't have a pointer to a reference, which might be needed internally in the container's code. > I found that one of the reasons is that reference cannot be re-initialized. > If this is true then why the "T * const" may be stored in STL containers ? A pointer is copyable value, and when stored it's an object. • • • Let's say that you want a vector of references to objects of the same type. Since you can't do that, simply store raw pointers: #include <iostream> #include <vector> using namespace std; auto main() -> int { int a = 100, b = 200, c = 300; vector<int*> values; for( auto const p : {&a, &b, &c} ) { values.push_back( p ); } ++a; ++b; ++c; for( int const* const p : values ) { cout << *p << " "; } cout << endl; } Output: 101 201 301 Cheers & hth., - Alf |
| Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk>: Sep 19 06:19PM +0100 > If this is true then why the "T * const" may be stored in STL containers ? > Please write me why references cannot be stored in STL containers. > thanks for help You won't get very far trying to use std::vector with "T* const" or any other const value_type. /Flibble |
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Sep 19 08:34PM +0200 > Could you please explain me why references cannot be stored in STL containers. They can't be stored DIRECTLY in containers. Most containers, and in particular those in the standard library, don't support reference element type because it would need extra machinery and interface semantics to handle the not-object-ness of references, e.g. that you can't have a pointer to a reference, which might be needed internally in the container's code. > I found that one of the reasons is that reference cannot be re-initialized. > If this is true then why the "T * const" may be stored in STL containers ? A pointer is copyable value, and when stored it's an object. • • • Let's say that you want a vector of references to objects of the same type. Since you can't do that, simply store raw pointers: #include <iostream> #include <vector> using namespace std; auto main() -> int { int a = 100, b = 200, c = 300; vector<int*> values; for( auto const p : {&a, &b, &c} ) { values.push_back( p ); } ++a; ++b; ++c; for( int const* const p : values ) { cout << *p << " "; } cout << endl; } Output: 101 201 301 Cheers & hth., - Alf |
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