etl/docs/utilities/mem_cast.md
2026-04-21 09:31:04 +02:00

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title
mem_cast

{{< callout type="info">}} Header: mem_cast.h Since: 20.11.0
{{< /callout >}}

Helper classes that simplify the interpretation of memory blocks.
The member functions contain both compile and run time error checks for correct sized buffers.

etl::mem_cast
etl::mem_cast_ptr
etl::mem_cast_types

Error types

class mem_cast_exception : public etl::exception

The base exception type for mem_cast types.

class mem_cast_size_exception : public etl::mem_cast_exception

The exception type when the type size is too large.

class mem_cast_nullptr_exception : public etl::mem_cast_exception

The exception type when the buffer pointer is null.

mem_cast

template <size_t Size, size_t Alignment>
class mem_cast

The class is parameterised by the required memory block size and alignment.

Member constants

static ETL_CONSTANT size_t Size;
static ETL_CONSTANT size_t Alignment;

Member functions

mem_cast()

Default constructor.
The internal memory block contents are undefined.


template <size_t Other_Size, size_t Other_Alignment>
mem_cast(const mem_cast<Other_Size, Other_Alignment>& other)

Copy constructor.
Copies the contents of the source buffer.
Static asserts if the other buffer is not large enough.


template <size_t Other_Size, size_t Other_Alignment>
mem_cast& operator =(const mem_cast<Other_Size, Other_Alignment>& rhs)

Assignment operator.
Static asserts if the rhs buffer is not large enough.


template <typename T>
void assign(const T& value)

Assign from value.
Static asserts if the buffer is not large enough.


template <typename T>
void assign_at_offset(size_t offset, const T& value)

Assign from value at an offset from the start of the memory block.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T, size_t Offset>
void assign_at_offset(const T& value)

Assign from value at an offset from the start of the memory block.
Static asserts if the buffer is not large enough.


template <typename T, typename... TArgs>
void emplace(TArgs... args)

Emplace from parameters.
Static asserts if the buffer is not large enough.
C++11 or above.


template <typename T, typename... TArgs>
void emplace_at_offset(size_t offset, TArgs... args)

Emplace from parameters at an offset from the start of the memory block.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.
C++11 or above.


template <typename T, size_t Offset, typename... TArgs>
void emplace_at_offset(TArgs... args)

Emplace from parameters at an offset from the start of the memory block.
Static asserts if the buffer is not large enough.
C++11 or above.


template <typename T>
ETL_NODISCARD T& ref()

Get a reference to T.
Static asserts if the buffer is not large enough.


template <typename T>
ETL_NODISCARD const T& ref() const

Get a const reference to T.
Static asserts if the buffer is not large enough.


template <typename T>
ETL_NODISCARD T& ref_at_offset(size_t offset)

Get a reference to T at an offset from the start of the memory block (dynamic).
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T>
ETL_NODISCARD const T& ref_at_offset(size_t offset) const

Get a const reference to T at an offset from the start of the memory block (dynamic).
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T, size_t Offset>
ETL_NODISCARD T& ref_at_offset()

Get a reference to T at an offset from the start of the memory block (static).
Static asserts if the buffer is not large enough.


template <typename T, size_t Offset>
ETL_NODISCARD const T& ref_at_offset() const

Get a const reference to T at an offset from the start of the memory block (static).
Static asserts if the buffer is not large enough.


ETL_NODISCARD static ETL_CONSTEXPR size_t size()

Get the size of the buffer.


ETL_NODISCARD static ETL_CONSTEXPR size_t alignment()

Get the alignment of the buffer.


ETL_NODISCARD char* data()

Get a pointer to the internal buffer.


ETL_NODISCARD const char* data() const

Get a const pointer to the internal buffer

mem_cast_ptr

This class contains a pointer to an external memory block.

class mem_cast_ptr

Member constants

static ETL_CONSTANT size_t Undefined_Size;

Member functions

mem_cast_ptr()

Default constructor.
The internal pointer to the memory block is initialised as nullptr.
The size is defined as Undefined_Size.

mem_cast_ptr(const mem_cast_ptr& other)

Copy constructor.
Copies the memory block pointer, not the contents of the memory block.


mem_cast_ptr& operator =(const mem_cast_ptr& rhs)

Assignment operator.
Copies the memory block pointer, not the contents of the memory block.


template <typename T>
void assign(const T& value)

Assign from value.
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T>
void assign_at_offset(size_t offset, const T& value)

Assign from value at an offset from the start of the memory block.
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T, size_t Offset>
void assign_at_offset(const T& value)

Assign from value at an offset from the start of the memory block.


template <typename T, typename... TArgs>
void emplace(TArgs... args)

Emplace from parameters.
C++11 or above.


template <typename T, typename... TArgs>
void emplace_at_offset(size_t offset, TArgs... args)

Emplace from parameters at offset.
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.
C++11 or above.


template <typename T, size_t Offset, typename... TArgs>
void emplace_at_offset(TArgs... args)

Emplace from parameters at offset.
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.
C++11 or above.


template <typename T>
ETL_NODISCARD T& ref()

Get a reference to T.
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T>
ETL_NODISCARD const T& ref() const

Get a const reference to T.
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an ETL_ASSERT if the buffer is not large enough.


template <typename T>
ETL_NODISCARD T& ref_at_offset(size_t offset)

Get a reference to T at an offset from the start of the memory block (dynamic). Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null. Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T>
ETL_NODISCARD const T& ref_at_offset(size_t offset) const

Get a const reference to T at offset (dynamic).
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T, size_t Offset>
ETL_NODISCARD T& ref_at_offset()

Get a reference to T at an offset from the start of the memory block (static).
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


template <typename T, size_t Offset>
ETL_NODISCARD const T& ref_at_offset() const

Get a const reference to T at an offset from the start of the memory block (static).
Raises an etl::mem_cast_nullptr_exception ETL_ASSERT if the memory block pointer is null.
Raises an etl::mem_cast_size_exception ETL_ASSERT if the buffer is not large enough.


ETL_NODISCARD size_t size() const

Get the size of the buffer.


ETL_NODISCARD size_t alignment() const

Get the alignment of the buffer.


void data(char* pbuffer, size_t buffer_size = Undefined_Size)

Set the pointer to the external buffer.
The default size is Undefined_Size.


ETL_NODISCARD char* data()

Get a pointer to the internal buffer.


ETL_NODISCARD const char* data() const

Get a const pointer to the internal buffer

mem_cast_types

A variant of etl::mem_cast that deduces the size and alignment from the supplied list of types.

C++03

template <typename T1,         typename T2  = char, typename T3  = char, typename T4  = char,
          typename T5  = char, typename T6  = char, typename T7  = char, typename T8  = char,
          typename T9  = char, typename T10 = char, typename T11 = char, typename T12 = char,
          typename T13 = char, typename T14 = char, typename T15 = char, typename T16 = char>
struct mem_cast_types :
  public etl::mem_cast<etl::largest<T1, T2, T3, T4, T5, T6, T7, T8, 
                                    T9, T10, T11, T12, T13, T14, T15, T16>::size,
                       etl::largest<T1, T2, T3, T4, T5, T6, T7, T8,
                                    T9, T10, T11, T12, T13, T14, T15, T16>::alignment>
{
};

C++11 and above

template <typename... TTypes>
using mem_cast_types = etl::mem_cast<etl::largest<TTypes...>::size, 
                                     etl::largest<TTypes...>::alignment>;