103 lines
3.8 KiB
Markdown
103 lines
3.8 KiB
Markdown
# <small>nlohmann::basic_json::</small>begin
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```cpp
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iterator begin() noexcept;
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const_iterator begin() const noexcept;
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```
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Returns an iterator to the first element.
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<div class="nj-fig-wrap" markdown>
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<svg class="nj-fig nj-fig--range" viewBox="0 0 600 150" role="img" aria-labelledby="fig-be-title" xmlns="http://www.w3.org/2000/svg">
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<title id="fig-be-title">A row of fifteen elements followed by a dashed past-the-last position. begin() points to the first element and end() points to the past-the-last position.</title>
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<defs><marker id="fig-be-arrow" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto"><path class="fg-head" d="M0 1 L10 5 L0 9 z"/></marker></defs>
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<rect class="fg-cell" x="30" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="64" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="98" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="132" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="166" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="200" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="234" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="268" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="302" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="336" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="370" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="404" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="438" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="472" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell" x="506" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-cell fg-cell--end" x="540" y="62" width="30" height="30" rx="5"/>
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<rect class="fg-pill" x="15" y="8" width="60" height="24" rx="6"/>
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<text class="fg-pilltext" x="45" y="24">begin</text>
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<line class="fg-arrow" x1="45" y1="32" x2="45" y2="60" marker-end="url(#fig-be-arrow)"/>
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<rect class="fg-pill" x="531" y="8" width="48" height="24" rx="6"/>
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<text class="fg-pilltext" x="555" y="24">end</text>
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<line class="fg-arrow" x1="555" y1="32" x2="555" y2="60" marker-end="url(#fig-be-arrow)"/>
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<text class="fg-note fg-note--r" x="537" y="132">Past-the-last element</text>
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<line class="fg-arrow" x1="555" y1="124" x2="555" y2="96" marker-end="url(#fig-be-arrow)"/>
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</svg>
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</div>
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<p class="nj-caption" markdown>`begin()` points to the first element and `end()` to the position after the last element;
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the dashed cell is the past-the-last position, which must not be dereferenced.</p>
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## Return value
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iterator to the first element
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## Exception safety
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No-throw guarantee: this member function never throws exceptions.
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## Complexity
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Constant.
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## Examples
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??? example
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The following code shows an example for `begin()`.
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```cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using nlohmann::json;
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int main()
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{
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// create an array value
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json array = {1, 2, 3, 4, 5};
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// get an iterator to the first element
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json::iterator it = array.begin();
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// serialize the element that the iterator points to
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std::cout << *it << '\n';
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}
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```
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Output:
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```json
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1
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```
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## See also
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- [`end`](end.md) - returns an iterator to one past the last element
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- [`cbegin`](cbegin.md) - returns a const iterator to the first element
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- [`rbegin`](rbegin.md) - returns a reverse iterator to the last element
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- [`items`](items.md) - returns an iteration proxy to access keys and values during range-based for loops
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- [Iterators](../../features/iterators.md) - the article on iterators
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- [`basic_json_view::begin`](../basic_json_view/begin.md) - the same iteration on a zero-copy view (in document order,
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not sorted by key)
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## Version history
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- Added in version 1.0.0.
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