Databases
StackOverflow2013
Postsdbo
POHow to know whether std::iterator_traits<T>::value_type is defined
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow to know whether std::iterator_traits<T>::value_type is defined
    primarykey
    data
    text
    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/11898657/enable-if-iterator-as-a-default-template-parameter">enable_if iterator as a default template parameter?</a> </p> </blockquote> <p>I'm looking for solution to know at compile-time whether <code>std::iterator_traits&lt;T&gt;::value_type</code> is valid and defined. The problem with this is that std library forwards the declaration of value_type to the derived type in T:</p> <pre><code>typedef T::value_type value_type; </code></pre> <p>I need to know whether T::value_type is valid type or not in compile time to avoid errors related to value_type not existing. </p> <p>Please consider these examples:</p> <pre><code>std::iterator_traits&lt;int *&gt;::value_type; // OK - should return that value_type exists as it's defined in specialization of std::iterator_traits std::iterator_traits&lt;const int *&gt;::value_type; // OK - should return that value_type exists as it's defined in specialization of std::iterator_traits std::iterator_traits&lt;std::vector&lt;int&gt;::const_iterator&gt; &gt;::value_type; // OK - the value_type exists defined within std::vector&lt;int&gt;::const_iterator std::iterator_traits&lt;int&gt;::value_type; // ERROR - the value_type is not defined within int class - this is what I'm trying to avoid to resolve the value_type of. </code></pre> <p>I need the solution to be fully compliant with C++ standard and std library standard and compiler independent.</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USPavel Celba
    plurals
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTDuplicate
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow to know whether std::iterator_traits<T>::value_type is defined
      1. This table or related slice is empty.
      1. VTDownMod
    2. VO
      singulars
      1. POHow to know whether std::iterator_traits<T>::value_type is defined
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThis question I answered recently may be of help: http://stackoverflow.com/questions/11898657/enable-if-iterator-as-a-default-template-parameter/11899057#11899057
      singulars
      1. POHow to know whether std::iterator_traits<T>::value_type is defined
      1. USR. Martinho Fernandes
    2. CO@R.MartinhoFernandes: That looks like a duplicate, in fact.
      singulars
      1. POHow to know whether std::iterator_traits<T>::value_type is defined
      1. USNawaz
    3. COI think whole problem with this is that it returns that the iterator_category exists: typedef typename _Iter::iterator_category iterator_category; defined in std::iterator_traits<T> default. Your sfinae will return that it exists, that the problem.
      singulars
      1. POHow to know whether std::iterator_traits<T>::value_type is defined
      1. USPavel Celba
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload