Variable size/Set

Demonstrate how to specify the minimum size of a variable or a data type.

Ada

<lang ada> type Response is (Yes, No); -- Definition of an enumeration type with two values for Response'Size use 1; -- Setting the size of Response to 1 bit, rather than the default single byte size </lang>

C

<lang c>#include <stdint.h>

int_least32_t foo;</lang>

Here foo is a signed integer with at least 32 bits. stdint.h also defines minimum-width types for at least 8, 16, 32, and 64 bits, as well as unsigned integer types.

D

In D, any variables of static array of zero length has a size of zero. But such data is useless, as no base type element can be accessed. <lang d> typedef long[0] zeroLength ; writefln(zeroLength.sizeof) ; // print 0 </lang> NOTE: a dynamic array variable's size is always 8 bytes, 4(32-bit) for length and 4 for a reference pointer of the actual storage somewhere in runtime memory.
The proper candidates of minimum size variable are empty structure, 1-byte size data type variable (include byte, ubyte, char and bool), and void, they all occupy 1 byte. <lang d> byte b ; ubyte ub ; char c ; bool t ; </lang> bool is logically 1-bit size, but it actually occupy 1 byte.
void can't be declared alone, but void.sizeof gives 1.
An empty structure is logically zero size, but still occupy 1 byte. <lang d> struct Empty { } writefln(Empty.sizeof) ; // print 1 </lang>

Perl

I suppose you could use vec() or similar to twiddle a single bit. The thing is, as soon as you store this in a variable, the SV (the underlying C implementation of the most simple data type) already takes a couple dozen of bytes.

In Perl, memory is readily and happily traded for expressiveness and ease of use.

Python

For compatibility with the calling conventions of external C functions, the ctypes module has functions that map data types and sizes between Python and C:

ctypes type	C type	Python type
c_char	char	1-character string
c_wchar	wchar_t	1-character unicode string
c_byte	char	int/long
c_ubyte	unsigned char	int/long
c_short	short	int/long
c_ushort	unsigned short	int/long
c_int	int	int/long
c_uint	unsigned int	int/long
c_long	long	int/long
c_ulong	unsigned long	int/long
c_longlong	__int64 or long long	int/long
c_ulonglong	unsigned __int64 or unsigned long long	int/long
c_float	float	float
c_double	double	float
c_longdouble	long double	float
c_char_p	char * (NUL terminated)	string or None
c_wchar_p	wchar_t * (NUL terminated)	unicode or None
c_void_p	void *	int/long or None

Tcl

In Tcl, most values are (Unicode) strings. Their size is measured in characters, and the minimum size of a string is of course 0. However, one can arrange, via write traces, that the value of a variable is reformatted to bigger size. Examples, from an interactive tclsh session: <lang Tcl>% proc format_trace {fmt _var el op} {upvar 1 $_var v; set v [format $fmt $v]}

% trace var foo w {format_trace %10s} % puts "/[set foo bar]/" / bar/

% trace var grill w {format_trace %-10s} % puts "/[set grill bar]/" /bar /</lang> ..or limit its size to a certain length: <lang Tcl>% proc range_trace {n _var el op} {upvar 1 $_var v; set v [string range $v 0 [incr n -1]]}

% trace var baz w {range_trace 2} % set baz Frankfurt Fr</lang>