Is there some differences about the size of intrinsic types in C++,
compared to C ?
Vincent Torri
On Mon, 28 Nov 2005, Nelson H. F. Beebe wrote:
> John Love-Jensen <eljay@xxxxxxxxx> writes on Mon, 28 Nov 2005 05:42:54 -0700 (MST):
>
> >> ...
> >> I'd have thought that on a 64-bit word-size architecture, int would be
> >> 64-bits big, long would be 128-bits big, and long long would be
> >> 256-bits big.
> >> ...
>
> No, the only requirement on C's integer data types is that
>
> sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(long) <= sizeof(long long)
>
> subject to minimum size requirements on each of them that are
> specified in the ISO C Standard. It is perfectly legal for all of
> these to have the same size, as long as they are big enough: on a
> 64-bit architecture, they all could be 64 bits long. See section 5.1
> of this book, which deserves to be on every serious C programmer's
> shelf:
>
> @String{pub-PH = "Pren{\-}tice-Hall"}
> @String{pub-PH:adr = "Upper Saddle River, NJ 07458, USA"}
>
> @Book{Harbison:2002:CRM,
> author = "Samuel P. {Harbison III} and Guy L. {Steele Jr.}",
> title = "{C} --- {A} Reference Manual",
> publisher = pub-PH,
> address = pub-PH:adr,
> edition = "Fifth",
> pages = "xviii + 533",
> year = "2002",
> ISBN = "0-13-089592-X",
> ISBN-13 = "978-0-13-089592-9",
> LCCN = "QA76.73.C15 H38 2002",
> bibdate = "Sat Mar 30 08:29:26 2002",
> price = "US\$45.00",
> URL = "http://www.CAReferenceManual.com/;
> http://www.phptr.com/ptrbooks/ptr_013089592X.html";,
> acknowledgement = ack-nhfb,
> }
>
> It is common on many Unix systems for int and long to have the same
> size, and on IBM PC DOS, some compilers made short and int the same
> size.
>
> Here is what the 1999 ISO C Standard has to say (notice the
> requirement phrase: ``Their ... values shall be equal or greater in
> magnitude...'') [I've replaced superscripts in inline comments by
> Fortran's power operator **]:
>
> >> ...
> >> 5.2.4.2.1 Sizes of integer types <limits.h>
> >>
> >> 1 The values given below shall be replaced by constant expressions
> >> suitable for use in #if preprocessing directives. Moreover,
> >> except for CHAR_BIT and MB_LEN_MAX, the following shall be
> >> replaced by expressions that have the same type as would an
> >> expression that is an object of the corresponding type converted
> >> according to the integer promotions. Their
> >> implementation-defined values shall be equal or greater in
> >> magnitude (absolute value) to those shown, with the same sign.
> >>
> >> -- number of bits for smallest object that is not a bit-field (byte)
> >> CHAR_BIT 8
> >>
> >> -- minimum value for an object of type signed char
> >> SCHAR_MIN -127 // -(2**{7} - 1)
> >>
> >> -- maximum value for an object of type signed char
> >> SCHAR_MAX +127 // 2**7 - 1
> >>
> >> -- maximum value for an object of type unsigned char
> >> UCHAR_MAX 255 // 2**8 - 1
> >>
> >> -- minimum value for an object of type char
> >> CHAR_MIN see below
> >>
> >> -- maximum value for an object of type char
> >> CHAR_MAX see below
> >>
> >> -- maximum number of bytes in a multibyte character, for any supported locale
> >> MB_LEN_MAX 1
> >>
> >> -- minimum value for an object of type short int
> >> SHRT_MIN -32767 // -(2**15 - 1)
> >>
> >> -- maximum value for an object of type short int
> >> SHRT_MAX +32767 // 2**15 - 1
> >>
> >> -- maximum value for an object of type unsigned short int
> >> USHRT_MAX 65535 // 2**16 - 1
> >>
> >> -- minimum value for an object of type int
> >> INT_MIN -32767 // -(2**15 - 1)
> >>
> >> -- maximum value for an object of type int
> >> INT_MAX +32767 // 2**15 - 1
> >>
> >> -- maximum value for an object of type unsigned int
> >> UINT_MAX 65535 // 2**16 - 1
> >>
> >> -- minimum value for an object of type long int
> >> LONG_MIN -2147483647 // -(2**31 - 1)
> >>
> >> -- maximum value for an object of type long int
> >> LONG_MAX +2147483647 // 2**31 - 1
> >>
> >> -- maximum value for an object of type unsigned long int
> >> ULONG_MAX 4294967295 // 2**32 - 1
> >>
> >> -- minimum value for an object of type long long int
> >> LLONG_MIN -9223372036854775807 // -(2**63 - 1)
> >>
> >> -- maximum value for an object of type long long int
> >> LLONG_MAX +9223372036854775807 // 2**63 - 1
> >>
> >> -- maximum value for an object of type unsigned long long int
> >> ULLONG_MAX 18446744073709551615 // 2**64 - 1
> >>
> >> 2 If the value of an object of type char is treated as a signed
> >> integer when used in an expression, the value of CHAR_MIN shall
> >> be the same as that of SCHAR_MIN and the value of CHAR_MAX shall
> >> be the same as that of SCHAR_MAX. Otherwise, the value of
> >> CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same
> >> as that of UCHAR_MAX.15) The value UCHAR_MAX shall equal
> >> 2CHAR_BIT - 1.
> >> ...
>
> There are similar constraints on float, double, and long double: they
> can all be of identical size, provided that they satisfy minimum range
> and precision specified in the ISO C Standard. I have used systems
> where this was the case, and also, where a char was nine bits (four
> then fitting in a 36-bit word).
>
> C's constraints on the sizes of floating-point types are different
> from Fortran, where the size of DOUBLE PRECISION is required to be
> twice that of REAL: that is essential knowledge for proper storage
> alignment in EQUIVALENCE statements and COMMON blocks.
>
> -------------------------------------------------------------------------------
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> - University of Utah FAX: +1 801 581 4148 -
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>
