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168 lines
3.5 KiB
Markdown
168 lines
3.5 KiB
Markdown
---
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title: "queue"
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---
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{{< callout >}}
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Header: `queue.h`
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{{< /callout >}}
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A fixed capacity queue.
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```cpp
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etl::queue<typename T,
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const size_t SIZE,
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const size_t MEMORY_MODEL = etl::memory_model::MEMORY_MODEL_LARGE>
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```
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Inherits from `etl::iqueue<T>`.
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`etl::iqueue` may be used as a size independent pointer or reference type for any `etl::queue` instance.
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The memory model determines the type used internally for indexes and size, to allow for the most efficient implementation for the application.
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## Maximum queue sizes
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```cpp
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MEMORY_MODEL_SMALL 255
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MEMORY_MODEL_MEDIUM 65535
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MEMORY_MODEL_LARGE 2147483647
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MEMORY_MODEL_HUGE 9223372036854775807
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```
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See `memory_model.h`
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## Member types
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value_type T
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size_type <based on memory model>
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pointer value_type*
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const_pointer const value_type*
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reference value_type&
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const_reference const value_type&
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rvalue_reference value_type&&
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## Constructor
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etl::queue<typename T, const size_t SIZE>()
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## Element access
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```cpp
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T& front()
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const T& front() const
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```
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**Description**
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Returns a reference or const reference to the first element.
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---
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```cpp
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T& back()
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const T& back() const
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```
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**Description**
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Returns a reference or const reference to the last element.
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## Capacity
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```cpp
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bool empty() const
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```
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**Description**
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Returns true if the size of the queue is zero, otherwise false.
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---
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```cpp
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bool full() const
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```
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**Description**
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Returns true if the size of the queue is SIZE, otherwise false.
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---
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```cpp
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size_type size() const
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```
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**Description**
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Returns the size of the queue.
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---
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```cpp
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size_type available() const
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```
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**Description**
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Returns the remaining available capacity in the queue.
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---
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```cpp
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ETL_CONSTEXPR size_type max_size() const
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```
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**Description**
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Returns the maximum possible size of the queue.
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---
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```cpp
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ETL_CONSTEXPR size_type capacity() const
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```
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**Description**
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Returns the maximum possible size of the queue.
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## Modifiers
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```cpp
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void push(const_reference value)
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void push(rvalue_reference value)
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```
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**Description**
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Pushes a value to the back of the queue.
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Emits an `etl::queue_full` if the queue is full and `ETL_CHECK_PUSH_POP` is defined. If asserts or exceptions are not enabled then undefined behaviour occurs.
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---
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### C++03
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```cpp
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void emplace(const T1& value1)
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void emplace(const T1& value1, const T2& value2)
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void emplace(const T1& value1, const T2& value2, const T3& value3)
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void emplace(const T1& value1, const T2& value2, const T3& value3, const T4& value4)
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```
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**Description**
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Constructs an item in the the queue 'in place'.
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Emits an `etl::queue_full` if the queue is full and `ETL_CHECK_PUSH_POP` is defined. If asserts or exceptions are not enabled then undefined behaviour occurs.
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### C++11
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```cpp
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void emplace(Args&&… args)
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```
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**Description**
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Constructs an item in the the queue 'in place'.
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Emits an `etl::queue_full` if the queue is full and `ETL_CHECK_PUSH_POP` is defined. If asserts or exceptions are not enabled then undefined behaviour occurs.
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---
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```cpp
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void pop()
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```
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**Description**
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Pop a value from the front of the list.
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Emits an `etl::queue_empty` if the queue is empty and `ETL_CHECK_PUSH_POP` is defined. Undefined behaviour if the queue is empty.
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---
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```cpp
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void pop_into(TContainer& destination)
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```
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**Description**
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Pop a value from the front of the list and places it in destination.
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Emits an `etl::queue_empty` if the queue is empty and `ETL_CHECK_PUSH_POP` is defined. Undefined behaviour if the queue is empty.
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---
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```cpp
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void clear()
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```
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**Description**
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Clears the queue to a size of zero.
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