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Preface armclang Command-line Options Compiler-specific Keywords and Operators Compiler-specific Function, Variable, and Type Att Function attributes __attribute__((always_inline)) function attribute __attribute__((cmse_nonsecure_call)) function attr __attribute__((cmse_nonsecure_entry)) function att __attribute__((const)) function attribute __attribute__((constructor(priority))) function at __attribute__((format_arg(string-index))) function __attribute__((interrupt("type"))) function attrib __attribute__((malloc)) function attribute __attribute__((naked)) function attribute __attribute__((noinline)) function attribute __attribute__((nonnull)) function attribute __attribute__((noreturn)) function attribute __attribute__((nothrow)) function attribute __attribute__((pcs("calling_convention"))) functio __attribute__((pure)) function attribute __attribute__((section("name"))) function attribut __attribute__((unused)) function attribute __attribute__((used)) function attribute __attribute__((value_in_regs)) function attribute __attribute__((visibility("visibility_type"))) fun __attribute__((weak)) function attribute __attribute__((weakref("target"))) function attrib Type attributes __attribute__((aligned)) type attribute __attribute__((packed)) type attribute __attribute__((transparent_union)) type attribute Variable attributes __attribute__((alias)) variable attribute __attribute__((aligned)) variable attribute __attribute__((deprecated)) variable attribute __attribute__((packed)) variable attribute __attribute__((section("name"))) variable attribut __attribute__((unused)) variable attribute __attribute__((used)) variable attribute __attribute__((visibility("visibility_type"))) var __attribute__((weak)) variable attribute __attribute__((weakref("target"))) variable attrib Compiler-specific Intrinsics Compiler-specific Pragmas Other Compiler-specific Features Standard C Implementation Definition Standard C++ Implementation Definition armclang Integrated Assembler armclang Inline Assembler

__attribute__((packed)) variable attribute

3.32 __attribute__((packed)) variable attribute

You can specify the packed variable attribute on fields that are members of a structure or union. It specifies that a member field has the smallest possible alignment. That is, one byte for a variable field, and one bit for a bitfield, unless you specify a larger value with the aligned attribute.

Example

struct
{
    char a;
    int b __attribute__((packed));
} Variable_Attributes_packed_0;

Note:

You must access a packed member of a structure or union directly from a variable of the structure or union. Taking the address of such a member produces a normal pointer which might be unaligned. The compiler assumes that the pointer is aligned. Dereferencing such a pointer can be unsafe even when unaligned accesses are supported by the target, because certain instructions always require word-aligned addresses.

Note:

If you take the address of a packed member, in most cases, the compiler generates a warning.
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