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langref: clarify struct memory layout

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Andrew Kelley 2023-10-30 16:27:12 -07:00
parent 1880c799ae
commit ffaeb45333
1 changed files with 6 additions and 7 deletions
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doc/langref.html.in
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@ -3316,10 +3316,12 @@ test "default struct initialization fields" {
{#header_close#}
{#header_open|extern struct#}
<p>An {#syntax#}extern struct{#endsyntax#} has in-memory layout guaranteed to match the
C ABI for the target.</p>
<p>This kind of struct should only be used for compatibility with the C ABI. Every other
use case should be solved with {#link|packed struct#} or normal {#link|struct#}.</p>
<p>An {#syntax#}extern struct{#endsyntax#} has in-memory layout matching
the C ABI for the target.</p>
<p>If well-defined in-memory layout is not required, {#link|struct#} is a better choice
because it places fewer restrictions on the compiler.</p>
<p>See {#link|packed struct#} for a struct that has the ABI of its backing integer,
which can be useful for modeling flags.</p>
{#see_also|extern union|extern enum#}
{#header_close#}
@ -3338,9 +3340,6 @@ test "default struct initialization fields" {
<li>An {#link|enum#} field uses exactly the bit width of its integer tag type.</li>
<li>A {#link|packed union#} field uses exactly the bit width of the union field with
the largest bit width.</li>
<li>Non-ABI-aligned fields are packed into the smallest possible
ABI-aligned integers in accordance with the target endianness.
</li>
</ul>
<p>
This means that a {#syntax#}packed struct{#endsyntax#} can participate