### 17.6 Layout of Source Language Data Types

These macros define the sizes and other characteristics of the standard basic data types used in programs being compiled. Unlike the macros in the previous section, these apply to specific features of C and related languages, rather than to fundamental aspects of storage layout.

— Macro: INT_TYPE_SIZE

> A C expression for the size in bits of the type `int` on the target machine. If you don't define this, the default is one word.

— Macro: SHORT_TYPE_SIZE

> A C expression for the size in bits of the type `short` on the target machine. If you don't define this, the default is half a word. (If this would be less than one storage unit, it is rounded up to one unit.)

— Macro: LONG_TYPE_SIZE

> A C expression for the size in bits of the type `long` on the target machine. If you don't define this, the default is one word.

— Macro: ADA_LONG_TYPE_SIZE

> On some machines, the size used for the Ada equivalent of the type `long` by a native Ada compiler differs from that used by C. In that situation, define this macro to be a C expression to be used for the size of that type. If you don't define this, the default is the value of `LONG_TYPE_SIZE`.

— Macro: LONG_LONG_TYPE_SIZE

> A C expression for the size in bits of the type `long long` on the target machine. If you don't define this, the default is two words. If you want to support GNU Ada on your machine, the value of this macro must be at least 64.

— Macro: CHAR_TYPE_SIZE

> A C expression for the size in bits of the type `char` on the target machine. If you don't define this, the default is `BITS_PER_UNIT`.

— Macro: BOOL_TYPE_SIZE

> A C expression for the size in bits of the C++ type `bool` and C99 type `_Bool` on the target machine. If you don't define this, and you probably shouldn't, the default is `CHAR_TYPE_SIZE`.

— Macro: FLOAT_TYPE_SIZE

> A C expression for the size in bits of the type `float` on the target machine. If you don't define this, the default is one word.

— Macro: DOUBLE_TYPE_SIZE

> A C expression for the size in bits of the type `double` on the target machine. If you don't define this, the default is two words.

— Macro: LONG_DOUBLE_TYPE_SIZE

> A C expression for the size in bits of the type `long double` on the target machine. If you don't define this, the default is two words.

— Macro: SHORT_FRACT_TYPE_SIZE

> A C expression for the size in bits of the type `short _Fract` on the target machine. If you don't define this, the default is `BITS_PER_UNIT`.

— Macro: FRACT_TYPE_SIZE

> A C expression for the size in bits of the type `_Fract` on the target machine. If you don't define this, the default is `BITS_PER_UNIT * 2`.

— Macro: LONG_FRACT_TYPE_SIZE

> A C expression for the size in bits of the type `long _Fract` on the target machine. If you don't define this, the default is `BITS_PER_UNIT * 4`.

— Macro: LONG_LONG_FRACT_TYPE_SIZE

> A C expression for the size in bits of the type `long long _Fract` on the target machine. If you don't define this, the default is `BITS_PER_UNIT * 8`.

— Macro: SHORT_ACCUM_TYPE_SIZE

> A C expression for the size in bits of the type `short _Accum` on the target machine. If you don't define this, the default is `BITS_PER_UNIT * 2`.

— Macro: ACCUM_TYPE_SIZE

> A C expression for the size in bits of the type `_Accum` on the target machine. If you don't define this, the default is `BITS_PER_UNIT * 4`.

— Macro: LONG_ACCUM_TYPE_SIZE

> A C expression for the size in bits of the type `long _Accum` on the target machine. If you don't define this, the default is `BITS_PER_UNIT * 8`.

— Macro: LONG_LONG_ACCUM_TYPE_SIZE

> A C expression for the size in bits of the type `long long _Accum` on the target machine. If you don't define this, the default is `BITS_PER_UNIT * 16`.

— Macro: LIBGCC2_GNU_PREFIX

> This macro corresponds to the `TARGET_LIBFUNC_GNU_PREFIX` target hook and should be defined if that hook is overriden to be true. It causes function names in libgcc to be changed to use a `__gnu_` prefix for their name rather than the default `__`. A port which uses this macro should also arrange to use `t-gnu-prefix` in the libgcc `config.host`.

— Macro: TARGET_FLT_EVAL_METHOD

> A C expression for the value for `FLT_EVAL_METHOD` in `float.h`, assuming, if applicable, that the floating-point control word is in its default state. If you do not define this macro the value of `FLT_EVAL_METHOD` will be zero.

— Macro: WIDEST_HARDWARE_FP_SIZE

> A C expression for the size in bits of the widest floating-point format supported by the hardware. If you define this macro, you must specify a value less than or equal to the value of `LONG_DOUBLE_TYPE_SIZE`. If you do not define this macro, the value of `LONG_DOUBLE_TYPE_SIZE` is the default.

— Macro: DEFAULT_SIGNED_CHAR

> An expression whose value is 1 or 0, according to whether the type `char` should be signed or unsigned by default. The user can always override this default with the options `-fsigned-char` and `-funsigned-char`.

— Target Hook: bool TARGET_DEFAULT_SHORT_ENUMS (void)

> This target hook should return true if the compiler should give an `enum` type only as many bytes as it takes to represent the range of possible values of that type. It should return false if all `enum` types should be allocated like `int`.

> The default is to return false.

— Macro: SIZE_TYPE

> A C expression for a string describing the name of the data type to use for size values. The typedef name `size_t` is defined using the contents of the string.

> The string can contain more than one keyword. If so, separate them with spaces, and write first any length keyword, then `unsigned` if appropriate, and finally `int`. The string must exactly match one of the data type names defined in the function `c_common_nodes_and_builtins` in the file `c-family/c-common.c`. You may not omit `int` or change the order—that would cause the compiler to crash on startup.

> If you don't define this macro, the default is `"long unsigned int"`.

— Macro: SIZETYPE

> GCC defines internal types (`sizetype`, `ssizetype`, `bitsizetype` and `sbitsizetype`) for expressions dealing with size. This macro is a C expression for a string describing the name of the data type from which the precision of `sizetype` is extracted.

> The string has the same restrictions as `SIZE_TYPE` string.

> If you don't define this macro, the default is `SIZE_TYPE`.

— Macro: PTRDIFF_TYPE

> A C expression for a string describing the name of the data type to use for the result of subtracting two pointers. The typedef name `ptrdiff_t` is defined using the contents of the string. See `SIZE_TYPE` above for more information.

> If you don't define this macro, the default is `"long int"`.

— Macro: WCHAR_TYPE

> A C expression for a string describing the name of the data type to use for wide characters. The typedef name `wchar_t` is defined using the contents of the string. See `SIZE_TYPE` above for more information.

> If you don't define this macro, the default is `"int"`.

— Macro: WCHAR_TYPE_SIZE

> A C expression for the size in bits of the data type for wide characters. This is used in `cpp`, which cannot make use of `WCHAR_TYPE`.

— Macro: WINT_TYPE

> A C expression for a string describing the name of the data type to use for wide characters passed to `printf` and returned from `getwc`. The typedef name `wint_t` is defined using the contents of the string. See `SIZE_TYPE` above for more information.

> If you don't define this macro, the default is `"unsigned int"`.

— Macro: INTMAX_TYPE

> A C expression for a string describing the name of the data type that can represent any value of any standard or extended signed integer type. The typedef name `intmax_t` is defined using the contents of the string. See `SIZE_TYPE` above for more information.

> If you don't define this macro, the default is the first of `"int"`, `"long int"`, or `"long long int"` that has as much precision as `long long int`.

— Macro: UINTMAX_TYPE

> A C expression for a string describing the name of the data type that can represent any value of any standard or extended unsigned integer type. The typedef name `uintmax_t` is defined using the contents of the string. See `SIZE_TYPE` above for more information.

> If you don't define this macro, the default is the first of `"unsigned int"`, `"long unsigned int"`, or `"long long unsigned int"` that has as much precision as `long long unsigned int`.

— Macro: SIG_ATOMIC_TYPE
— Macro: INT8_TYPE
— Macro: INT16_TYPE
— Macro: INT32_TYPE
— Macro: INT64_TYPE
— Macro: UINT8_TYPE
— Macro: UINT16_TYPE
— Macro: UINT32_TYPE
— Macro: UINT64_TYPE
— Macro: INT_LEAST8_TYPE
— Macro: INT_LEAST16_TYPE
— Macro: INT_LEAST32_TYPE
— Macro: INT_LEAST64_TYPE
— Macro: UINT_LEAST8_TYPE
— Macro: UINT_LEAST16_TYPE
— Macro: UINT_LEAST32_TYPE
— Macro: UINT_LEAST64_TYPE
— Macro: INT_FAST8_TYPE
— Macro: INT_FAST16_TYPE
— Macro: INT_FAST32_TYPE
— Macro: INT_FAST64_TYPE
— Macro: UINT_FAST8_TYPE
— Macro: UINT_FAST16_TYPE
— Macro: UINT_FAST32_TYPE
— Macro: UINT_FAST64_TYPE
— Macro: INTPTR_TYPE
— Macro: UINTPTR_TYPE

> C expressions for the standard types `sig_atomic_t`, `int8_t`, `int16_t`, `int32_t`, `int64_t`, `uint8_t`, `uint16_t`, `uint32_t`, `uint64_t`, `int_least8_t`, `int_least16_t`, `int_least32_t`, `int_least64_t`, `uint_least8_t`, `uint_least16_t`, `uint_least32_t`, `uint_least64_t`, `int_fast8_t`, `int_fast16_t`, `int_fast32_t`, `int_fast64_t`, `uint_fast8_t`, `uint_fast16_t`, `uint_fast32_t`, `uint_fast64_t`, `intptr_t`, and `uintptr_t`. See `SIZE_TYPE` above for more information.

> If any of these macros evaluates to a null pointer, the corresponding type is not supported; if GCC is configured to provide `<stdint.h>` in such a case, the header provided may not conform to C99, depending on the type in question. The defaults for all of these macros are null pointers.

— Macro: TARGET_PTRMEMFUNC_VBIT_LOCATION

> The C++ compiler represents a pointer-to-member-function with a struct that looks like:

>                 struct {
>                   union {
>                     void (*fn)();
>                     ptrdiff_t vtable_index;
>                   };
>                   ptrdiff_t delta;
>                 };

> The C++ compiler must use one bit to indicate whether the function that will be called through a pointer-to-member-function is virtual. Normally, we assume that the low-order bit of a function pointer must always be zero. Then, by ensuring that the vtable_index is odd, we can distinguish which variant of the union is in use. But, on some platforms function pointers can be odd, and so this doesn't work. In that case, we use the low-order bit of the `delta` field, and shift the remainder of the `delta` field to the left.

> GCC will automatically make the right selection about where to store this bit using the `FUNCTION_BOUNDARY` setting for your platform. However, some platforms such as ARM/Thumb have `FUNCTION_BOUNDARY` set such that functions always start at even addresses, but the lowest bit of pointers to functions indicate whether the function at that address is in ARM or Thumb mode. If this is the case of your architecture, you should define this macro to `ptrmemfunc_vbit_in_delta`.

> In general, you should not have to define this macro. On architectures in which function addresses are always even, according to `FUNCTION_BOUNDARY`, GCC will automatically define this macro to `ptrmemfunc_vbit_in_pfn`.

— Macro: TARGET_VTABLE_USES_DESCRIPTORS

> Normally, the C++ compiler uses function pointers in vtables. This macro allows the target to change to use “function descriptors” instead. Function descriptors are found on targets for whom a function pointer is actually a small data structure. Normally the data structure consists of the actual code address plus a data pointer to which the function's data is relative.

> If vtables are used, the value of this macro should be the number of words that the function descriptor occupies.

— Macro: TARGET_VTABLE_ENTRY_ALIGN

> By default, the vtable entries are void pointers, the so the alignment is the same as pointer alignment. The value of this macro specifies the alignment of the vtable entry in bits. It should be defined only when special alignment is necessary. */

— Macro: TARGET_VTABLE_DATA_ENTRY_DISTANCE

> There are a few non-descriptor entries in the vtable at offsets below zero. If these entries must be padded (say, to preserve the alignment specified by `TARGET_VTABLE_ENTRY_ALIGN`), set this to the number of words in each data entry.