C166 结构按字节访问的设置

PACK Compiler Directive

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Abbreviation	None.
Arguments	A decimal number (1 or 2) enclosed in parentheses.
Default	PACK(1)
µVision	Options — C166 â€” Misc Controls.
Description	The PACK directive causes the compiler to generate byte-aligned or half-word-aligned structures. This is useful when exchanging data with other systems where no alignment is required.  Note The compiler generates considerably more code to access byte-aligned words. For this reason, PACK(1)should be used only when necessary. By default, the compiler assumes that structure members are aligned on word boundaries. If you use PACK(1) some structure members may be aligned on byte boundaries. The BYTEALIGN directive supports pointers to structure members that are aligned on byte boundaries.
See Also	BYTEALIGN
Example	#pragma pack(1) /* byte alignment */ #pragma bytealign /* ptrs to byte-aligned objects */ struct s1 { int i1; // i1 has offset 0 char c1; // c1 has offset 2 int i2; // i2 has offset 3 char c2; // c2 has offset 5 int i3; // i3 has offset 6 char z1; // z1 has offset 8 }; #pragma pack() /* reset to default alignment */ struct s2 { int i1; // i1 has offset 0 char c1; // c1 has offset 2 int i2; // i2 has offset 4 char c2; // c2 has offset 6 int i3; // i3 has offset 8 char z1; // z1 has offset 10 };

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