From Jason Turner

[dcl.align]

C++17 → C++20 2.5 KB 25 lines
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Archived: C++17 | C++20
Markdown: C++17 | C++20
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  1. tmp/tmpo0_uu59z/{from.md → to.md} +9 -12
tmp/tmpo0_uu59z/{from.md → to.md} RENAMED
@@ -1,29 +1,26 @@
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  ### Alignment specifier <a id="dcl.align">[[dcl.align]]</a>
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  An *alignment-specifier* may be applied to a variable or to a class data
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  member, but it shall not be applied to a bit-field, a function
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- parameter, or an *exception-declaration* ([[except.handle]]). An
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- *alignment-specifier* may also be applied to the declaration or
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- definition of a class (in an *elaborated-type-specifier* (
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- [[dcl.type.elab]]) or *class-head* (Clause  [[class]]), respectively)
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- and to the declaration or definition of an enumeration (in an
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- *opaque-enum-declaration* or *enum-head*, respectively ([[dcl.enum]])).
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- An *alignment-specifier* with an ellipsis is a pack expansion (
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- [[temp.variadic]]).
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  When the *alignment-specifier* is of the form `alignas(`
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  *constant-expression* `)`:
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  - the *constant-expression* shall be an integral constant expression
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- - if the constant expression does not evaluate to an alignment value (
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- [[basic.align]]), or evaluates to an extended alignment and the
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  implementation does not support that alignment in the context of the
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  declaration, the program is ill-formed.
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  An *alignment-specifier* of the form `alignas(` *type-id* `)` has the
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- same effect as `alignas({}alignof(` *type-id* `))` ([[expr.alignof]]).
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  The alignment requirement of an entity is the strictest nonzero
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  alignment specified by its *alignment-specifier*s, if any; otherwise,
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  the *alignment-specifier*s have no effect.
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@@ -56,11 +53,11 @@ different *alignment-specifier*s in different translation units.
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  ``` cpp
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  // Translation unit #1:
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  struct S { int x; } s, *p = &s;
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  // Translation unit #2:
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- struct alignas(16) S; // error: definition of S lacks alignment, no diagnostic required
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  extern S* p;
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  ```
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  — *end example*]
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  ### Alignment specifier <a id="dcl.align">[[dcl.align]]</a>
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  An *alignment-specifier* may be applied to a variable or to a class data
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  member, but it shall not be applied to a bit-field, a function
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+ parameter, or an *exception-declaration* [[except.handle]]. An
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+ *alignment-specifier* may also be applied to the declaration of a class
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+ (in an *elaborated-type-specifier* [[dcl.type.elab]] or *class-head*
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+ [[class]], respectively). An *alignment-specifier* with an ellipsis is a
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+ pack expansion [[temp.variadic]].
 
 
 
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  When the *alignment-specifier* is of the form `alignas(`
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  *constant-expression* `)`:
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  - the *constant-expression* shall be an integral constant expression
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+ - if the constant expression does not evaluate to an alignment value
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+ [[basic.align]], or evaluates to an extended alignment and the
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  implementation does not support that alignment in the context of the
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  declaration, the program is ill-formed.
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  An *alignment-specifier* of the form `alignas(` *type-id* `)` has the
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+ same effect as `alignas({}alignof(` *type-id* `))` [[expr.alignof]].
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  The alignment requirement of an entity is the strictest nonzero
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  alignment specified by its *alignment-specifier*s, if any; otherwise,
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  the *alignment-specifier*s have no effect.
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  ``` cpp
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  // Translation unit #1:
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  struct S { int x; } s, *p = &s;
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  // Translation unit #2:
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+ struct alignas(16) S; // ill-formed, no diagnostic required: definition of S lacks alignment
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  extern S* p;
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  ```
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  — *end example*]
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