[#BloombergLP-bslstl-IteratorUtil-insertDistance]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::xref:BloombergLP/bslstl/IteratorUtil.adoc[IteratorUtil]::insertDistance
:relfileprefix: ../../../
:mrdocs:

Return the number of elements to account for when range‐inserting.

== Synopsis

Declared in `<bslstl_iteratorutil.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_INPUT_ITERATOR,
    class t_SENTINEL>
static
bsl::iterator_traits<t_INPUT_ITERATOR>::difference_type
insertDistance(
    t_INPUT_ITERATOR const& first,
    t_SENTINEL const& last);
----

== Description

Return 0 if the (template parameter) type `t_INPUT_ITERATOR` is limited to the standard input‐iterator category, otherwise return the number of elements reachable from the specified `first` to (but not including) the specified `last`. This function has a constant‐time complexity if the iterator category of `t_INPUT_ITERATOR` is strictly a standard input iterator, or is a random access iterator, otherwise it is linear in the length of the range `[first .. last)]`. The behavior is undefined unless `last` is reachable from `first`.

== Return Value

the number of elements in `[first .. last)]`, or 0 if distance cannot be calculated for the iterator category

== Parameters

[cols="1,4"]
|===
| Name| Description
| *first*
| beginning of the half‐open range
| *last*
| end of the half‐open range
|===


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