- What is '!cin'? - 4 Updates
- apply function and operator - 2 Updates
- C++ needs some help - 1 Update
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Nov 01 08:35AM +0100 On 10/31/2015 3:54 PM, Richard Damon wrote: [snip] > istreams define a member operator!() which is the equivalent to calling > fail() to see if something has gone wrong with the stream (like it > couldn't extract a string s1) Roughly, but the details are a bit different. C++ streams define conversion to boolean, and applying the built-in "!" operator invokes that conversion. In C++98 this was an implicitly invokable conversion to "void*". In C++11 and later it's an "explicit" conversion to "bool", with special rules that allow such a conversion to be implicitly invoked in a context requiring a "bool". C++14 §4/4 «Certain language constructs require that an expression be converted to a Boolean value. An expression e appearing in such a context is said to be /contextually converted/ to bool and is well-formed if and only if the declaration bool t(e); is well-formed, for some invented temporary variable t (8.5).» Essentially, writing "!stream" is equivalent to writing "stream.fail()". Worth noting, that "stream.good()" is not the opposite of "stream.fail()", and that the conversion to boolean is based on "fail()". Cheers, - Alf |
| fl <rxjwg98@gmail.com>: Nov 01 10:59AM -0800 On Sunday, November 1, 2015 at 2:35:28 AM UTC-5, Alf P. Steinbach wrote: > "stream.fail()", and that the conversion to boolean is based on "fail()". > Cheers, > - Alf Great thanks. I use MSVC 2010. What version is it, C++11, or C++14? How can I know that? |
| fl <rxjwg98@gmail.com>: Nov 01 11:02AM -0800 On Sunday, November 1, 2015 at 2:35:28 AM UTC-5, Alf P. Steinbach wrote: > "stream.fail()", and that the conversion to boolean is based on "fail()". > Cheers, > - Alf I am a little confused about the description. "!stream" is an explicit type or an implicit type? Thanks, In C++11 and later it's an "explicit" conversion to "bool", with special rules that allow such a conversion to be implicitly invoked in a context requiring a "bool". |
| Paavo Helde <myfirstname@osa.pri.ee>: Nov 01 02:46PM -0600 fl <rxjwg98@gmail.com> wrote in > Great thanks. I use MSVC 2010. What version is it, C++11, or C++14? > How can I know that? http://en.cppreference.com/w/cpp/compiler_support In this table, MSVC2010 appears as MSVC 10.x (see https://en.wikipedia.org/wiki/Visual_C%2B%2B). It does indeed contain some C++11 features, but not the "Explicit conversion operators" feature discussed in this thread. hth Paavo |
| asetofsymbols@gmail.com: Nov 01 01:13AM -0800 Wouter wrote: google "c++ lambda" Wouter ------- I find in internet some example of anonymous function in C++ In our example will be something as x.apply( u32 (u32 z)[](2*z) ) or something as above: But I think the matlab way is better x.apply( @(z) 2*z ) Because is more short: Will be the compiler find the right function: if there are 2 or more functions that are ok than not compile and add type in function For me the best would be x.apply(2*α) Where α is a variable... if one has 2 variables just write 2*α+β as (x,y)->(2*x+y) |
| asetofsymbols@gmail.com: Nov 01 01:16AM -0800 First 10 Greek letters lowercase as argument for anonymous function |
| woodbrian77@gmail.com: Oct 31 09:28PM -0700 On Saturday, October 31, 2015 at 12:22:52 PM UTC-5, Jorgen Grahn wrote: > > Alphabetical would be more logical. > However, what matters is what rules Wikipedia has around > such things. Either alphabetical or chronological would be an improvement. If Java supporters insist on a long, boring description, they should be willing to let shorter and sweeter descriptions be placed before them. |
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