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Jul 7, 2022
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Update pack.md #4026

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2 changes: 1 addition & 1 deletion docs/preprocessor/pack.md
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Expand Up @@ -38,7 +38,7 @@ The statement `#pragma pack (pop, r1, 2)` is equivalent to `#pragma pack (pop, r

## Remarks

To *pack* a class is to place its members directly after each other in memory. It can mean that some or all members can be aligned on a boundary smaller than the default alignment of the target architecture. **`pack`** gives control at the data-declaration level. It differs from compiler option [`/Zp`](../build/reference/zp-struct-member-alignment.md), which only provides module-level control. **pack** takes effect at the first **`struct`**, **`union`**, or **`class`** declaration after the pragma is seen. **`pack`** has no effect on definitions. Calling **`pack`** with no arguments sets *`n`* to the value set in the compiler option **`/Zp`**. If the compiler option isn't set, the default value is 8 for x86, ARM, and ARM64. The default is 16 for x64 native.
To *pack* a class is to place its members directly after each other in memory. It can mean that some or all members can be aligned on a boundary smaller than the default alignment of the target architecture. **`pack`** gives control at the data-declaration level. It differs from compiler option [`/Zp`](../build/reference/zp-struct-member-alignment.md), which only provides module-level control. **pack** takes effect at the first **`struct`**, **`union`**, or **`class`** declaration after the pragma is seen. **`pack`** has no effect on definitions. Calling **`pack`** with no arguments sets *`n`* to the value set in the compiler option **`/Zp`**. If the compiler option isn't set, the default value is 8 for x86, ARM, and ARM64. The default is 16 for x64 native and ARM64EC.

If you change the alignment of a structure, it may not use as much space in memory. However, you may see a loss of performance or even get a hardware-generated exception for unaligned access. You can modify this exception behavior by using [`SetErrorMode`](/windows/win32/api/errhandlingapi/nf-errhandlingapi-seterrormode).

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