How does C/C structure layout impact performance and memory efficiency?

Memory Allocation and Structure Layout in C/C

When defining a struct in C/C , such as the "test" struct:

<code class="c">struct test
{
   double height;
   int    age;
   char   gender;
}</code>

it is not guaranteed that the members (A.height, A.age, A.gender) will be stored contiguously in memory. This is due to a concept known as struct padding.

However, in some cases, members may be stored contiguously. For example, if the struct is defined as:

<code class="c">struct test
{
    char   gender;
    int    age;
    double height;
}</code>

the members are more likely to be contiguous. However, even in this case, there may be padding added after the "gender" member to align the struct to a specific boundary.

Memory Layout for Structures of Arrays and Arrays of Structures

There are two common data structures that involve structures and arrays: Structure of Arrays (SoA) and Array of Structures (AoS).

SoA (Structure of Arrays):

-----------------------------------------------------------------------------------
| double | double | double | *pad* | int | int | int | *pad* | char | char | char |
-----------------------------------------------------------------------------------

In SoA, the members of the struct are stored in contiguous arrays. This can be more efficient for operations that iterate over a specific member across all structs.

AoS (Array of Structures):

-----------------------------------------------------------------------------------
| double | int | char | *pad* | double | int | char | *pad* | double | int | char |
-----------------------------------------------------------------------------------

In AoS, each struct is stored as a contiguous block of memory. This can be more beneficial for accessing all members of a single struct together.

Trade-offs Between SoA and AoS:

• AoS: Better readability, potentially better cache locality
• SoA: Potential for vectorization, reduced memory usage

The above is the detailed content of How does C/C structure layout impact performance and memory efficiency?. For more information, please follow other related articles on the PHP Chinese website!