https://github.com/avakar/container_of
Type-safe inverse of pointer-to-member operators for C++11
https://github.com/avakar/container_of
cpp11 pointer-to-member
Last synced: about 2 months ago
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Type-safe inverse of pointer-to-member operators for C++11
- Host: GitHub
- URL: https://github.com/avakar/container_of
- Owner: avakar
- License: 0bsd
- Created: 2021-01-20T23:00:22.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2021-08-06T20:31:11.000Z (almost 4 years ago)
- Last Synced: 2025-04-12T19:57:47.207Z (about 2 months ago)
- Topics: cpp11, pointer-to-member
- Language: C++
- Homepage:
- Size: 6.84 KB
- Stars: 2
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# container_of
Type-safe inverse of pointer-to-member operators for C++11.
## Motivation
In C++, one can create a pointer to non-static data member of a structure.
The type of such a pointer is `T X::*`, where `X` is the type of the structure
and `T` is the type of the member. For example,
```cpp
struct point_t
{
int x;
int y;
};
int point_t::* mp = &point_t::y;
```
The pointer-to-member object effectively behaves as a type-safe offset,
you can use the `.*` operator to move from a pointer to the structure
to the pointer to its member.
```cpp
point_t point;
int * coord = &point.*mp;
assert(coord == &point.y);
```
However, C++ doesn't provide any way to recover the pointer to the structure,
given a pointer to its member and the appropriate pointer-to-member object.
This library provides `container_of` function that does exactly that.
```cpp
point_t * pt = container_of(coord, mp);
assert(pt == &point);
```
The function has therefore the same effect as
the `container_of` macro in the Linux kernel or `CONTAINING_RECORD` in Windows,
except that the member specification is an object that can be passed around.
You can now pass pointer-to-member objects around instead of member offsets.
## Getting started
The library is header-only. To use it, clone the repo somewhere
and add the `include` directory to your include path.
If you're using CMake, use the FetchContent module.
```cmake
FetchContent_Declare(
avakar.container_of
GIT_REPOSITORY https://github.com/avakar/container_of.git
GIT_TAG main
GIT_SHALLOW 1
)
FetchContent_MakeAvailable(avakar.container_of)
target_link_libraries(my_target PUBLIC avakar::container_of)
```
## Usage
Include ``, which provides the following function.
```cpp
template
X * avakar::container_of(T * p, T X::* mp) noexcept;
```
Both `p` and `mp` shall be non-null pointers.
The object pointed to by `p` shall be a member of an object of type `X`
corresponding to the member referred to by `mp`. `mp` shall not
refer to a member of a virtual base of `X` (such pointers cannot be
formed in standard C++, but Microsoft Visual Studio compiler
allows it as an extension). Otherwise, the behavior is undefined.