Anderson localization: Difference between revisions
en>Bibcode Bot m Adding 5 arxiv eprint(s), 0 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot |
|||
Line 1: | Line 1: | ||
{{C Standard Library}} | |||
In the [[C (programming language)|C programming language]], '''data types''' refers to an extensive system for declaring variables of different types. The language itself provides basic arithmetic types and syntax to build array and compound types. Several headers in the [[C standard library|standard library]] contain definitions of support types, that have additional properties, such as exact size, guaranteed.<ref>{{cite web | url=http://www.netrino.com/node/140 | title=Portable Fixed-Width Integers in C | first=Michael | last=Barr | date=2 December 2007 | accessdate=8 November 2011}}</ref><ref name=c99>{{cite book | url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf | title=ISO/IEC 9899:1999 specification | at=p. 264, § 7.18 ''Integer types''}}</ref> | |||
==Basic types== | |||
The C language provides many basic types. Most of them are formed from one of the four basic arithmetic type specifiers in C (<code>char</code>, <code>int</code>, <code>float</code> and <code>double</code>), and optional specifiers (<code>signed</code>, <code>unsigned</code>, <code>short</code>, <code>long</code>). All available basic arithmetic types are listed below: | |||
{| class="wikitable" style="font-size:0.90em; line-height:1.3em;" | |||
|- | |||
! style="width:14em;"| Type | |||
!| Explanation | |||
|- | |||
|| {{cpp|char}} || smallest addressable unit of the machine that can contain basic character set. It is an integer type. Actual type can be either signed or unsigned depending on the implementation. | |||
|- | |||
|| {{cpp|signed char}} || same size as <code>char</code>, but guaranteed to be signed. | |||
|- | |||
| {{cpp|unsigned char}} || same size as <code>char</code>, but guaranteed to be unsigned. | |||
|- | |||
| {{cpp|short}}<br>{{cpp|short int}}<br>{{cpp|signed short}}<br>{{cpp|signed short int}} || ''short'' signed integer type. At least 16 bits in size. | |||
|- | |||
| {{cpp|unsigned short}}<br>{{cpp|unsigned short int}} || same as <code>short</code>, but unsigned. | |||
|- | |||
| {{cpp|int}}<br>{{cpp|signed int}} || basic signed integer type. At least 16 bits in size. | |||
|- | |||
| {{cpp|unsigned}}<br>{{cpp|unsigned int}} || same as <code>int</code>, but unsigned. | |||
|- | |||
| {{cpp|long}}<br>{{cpp|long int}}<br>{{cpp|signed long}}<br>{{cpp|signed long int}} || ''long'' signed integer type. At least 32 bits in size. | |||
|- | |||
| {{cpp|unsigned long}}<br>{{cpp|unsigned long int}} || same as <code>long</code>, but unsigned. | |||
|- | |||
| {{cpp|long long}}<br>{{cpp|long long int}}<br>{{cpp|signed long long}}<br>{{cpp|signed long long int}} || ''long long'' signed integer type. At least 64 bits in size. Specified since the [[C99]] version of the standard. | |||
|- | |||
| {{cpp|unsigned long long}}<br>{{cpp|unsigned long long int}} || same as <code>long long</code>, but unsigned. Specified since the [[C99]] version of the standard. | |||
|- | |||
| {{cpp|float}} || single precision floating-point type. Actual properties unspecified (except minimum limits), however on most systems this is the [[Single-precision floating-point format|IEEE 754 single-precision binary floating-point format]]. This format is required by the optional Annex F "IEC 60559 floating-point arithmetic". | |||
|- | |||
| {{cpp|double}} || double precision floating-point type. Actual properties unspecified (except minimum limits), however on most systems this is the [[Double-precision floating-point format|IEEE 754 double-precision binary floating-point format]]. This format is required by the optional Annex F "IEC 60559 floating-point arithmetic". | |||
|- | |||
| {{cpp|long double}} || extended precision floating-point type. Actual properties unspecified. Unlike types {{cpp|float}} and {{cpp|double}}, it can be either [[Extended precision|80-bit floating point format]], the non-IEEE "double-double" or [[Quadruple-precision floating-point format|IEEE 754 quadruple-precision floating-point format]] if a higher precision format is provided, otherwise it is the same as {{cpp|double}}. See [[long double|the article on long double]] for details. | |||
|} | |||
The actual size of integer types varies by implementation. The standard only requires size relations between the data types and minimum sizes for each data type: | |||
The relation requirements are that the <code>long long</code> is not smaller than <code>long</code>, which is not smaller than <code>int</code>, which is not smaller than <code>short</code>. As <code>char</code>'s size is always the minimum supported data type, all other data types can't be smaller. | |||
The minimum size for <code>char</code> is 8 bit, the minimum size for <code>short</code> and <code>int</code> is 16 bit, for <code>long</code> it is 32 bit and <code>long long</code> must contain at least 64 bit. | |||
The type <code>int</code> should be the integer type that the target processor is most efficient working with. This allows great flexibility: for example, all types can be 64-bit. However, several different integer width schemes (data models) are popular. This is because the data model defines how different programs communicate, a uniform data model is used within a given operating system application interface.<ref>{{cite web|url=http://www.unix.org/version2/whatsnew/lp64_wp.html | title=64-Bit Programming Models: Why LP64? |publisher=The Open Group | accessdate=9 November 2011}}</ref> | |||
In practice it should be noted that <code>char</code> is usually 8 bits in size and <code>short</code> is usually 16 bits in size (as are their unsigned counterparts). This holds true for platforms as diverse as 1990s [[SunOS]] 4 Unix, Microsoft [[MS-DOS]], modern [[Linux]], and Microchip MCC18 for embedded 8 bit PIC microcontrollers. [[POSIX]] requires <code>char</code> to be exactly 8 bits in size. | |||
The actual size and behavior of floating-point types also vary by implementation. The only guarantee is that <code>long double</code> is not smaller than <code>double</code>, which is not smaller than <code>float</code>. Usually, the 32-bit and 64-bit [[IEEE floating point|IEEE 754]] binary floating-point formats are used, if supported by hardware. | |||
==={{anchor|stdbool.h}}Boolean type=== | |||
[[C99]] added a boolean (true/false) type (<code>_Bool</code>) which is defined in the <code><stdbool.h></code> header. Additionally, the standard requires that macros are defined to alias the type as <code>bool</code> as well as providing macros for <code>true</code> and <code>false</code>. | |||
==={{anchor|stddef.h}}Size and pointer difference types=== | |||
The C language provides the separate types <code>size_t</code> and <code>ptrdiff_t</code> to represent memory-related quantities. Existing types were deemed insufficient, because their size is defined according to the target processor's arithmetic capabilities, not the memory capabilities, such as available address space. Both of these types are defined in the <code><stddef.h></code> header (<code>cstddef</code> header in C++). | |||
<code>size_t</code> is used to represent the size of any object (including arrays) in the particular implementation. It is used as the return type of the <code>sizeof</code> operator. The maximum size of <code>size_t</code> is provided via <code>SIZE_MAX</code>, a macro constant which is defined in the <code><stdint.h></code> header (<code>cstdint</code> header in C++). It is guaranteed to be at least 65535. | |||
Note that <code>size_t</code> is unsigned, signed sizes can be represented by <code>ssize_t</code>. | |||
<code>ptrdiff_t</code> is used to represent the difference between pointers. | |||
==={{anchor|limits.h|float.h}}Interface to the properties of the basic types=== | |||
Information about the actual properties, such as size, of the basic arithmetic types, is provided via macro constants in two headers: <code><limits.h></code> header (<code>climits</code> header in C++) defines macros for integer types and <code><float.h></code> header (<code>cfloat</code> header in C++) defines macros for floating-point types. The actual values depend on the implementation. | |||
; Properties of integer types | |||
*<code>CHAR_BIT</code> – size of the {{cpp|char}} type in bits (at least 8 bits) | |||
*<code>SCHAR_MIN</code>, <code>SHRT_MIN</code>, <code>INT_MIN</code>, <code>LONG_MIN</code>, <code>LLONG_MIN</code><small>(C99)</small> – minimum possible value of signed integer types: {{cpp|signed char}}, {{cpp|signed short}}, {{cpp|signed int}}, {{cpp|signed long}}, {{cpp|signed long long}} | |||
*<code>SCHAR_MAX</code>, <code>SHRT_MAX</code>, <code>INT_MAX</code>, <code>LONG_MAX</code>, <code>LLONG_MAX</code><small>(C99)</small> – maximum possible value of signed integer types: {{cpp|signed char}}, {{cpp|signed short}}, {{cpp|signed int}}, {{cpp|signed long}}, {{cpp|signed long long}} | |||
*<code>UCHAR_MAX</code>, <code>USHRT_MAX</code>, <code>UINT_MAX</code>, <code>ULONG_MAX</code>, <code>ULLONG_MAX</code><small>(C99)</small> – maximum possible value of unsigned integer types: {{cpp|unsigned char}}, {{cpp|unsigned short}}, {{cpp|unsigned int}}, {{cpp|unsigned long}}, {{cpp|unsigned long long}} | |||
*<code>CHAR_MIN</code> – minimum possible value of {{cpp|char}} | |||
*<code>CHAR_MAX</code> – maximum possible value of {{cpp|char}} | |||
*<code>MB_LEN_MAX</code> – maximum number of bytes in a multibyte character | |||
; Properties of floating-point types | |||
*<code>FLT_MIN</code>, <code>DBL_MIN</code>, <code>LDBL_MIN</code> – minimum normalized positive value of {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_TRUE_MIN</code>, <code>DBL_TRUE_MIN</code>, <code>LDBL_TRUE_MIN</code> (C11) – minimum positive value of {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_MAX</code>, <code>DBL_MAX</code>, <code>LDBL_MAX</code> – maximum finite value of {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_ROUNDS</code> – rounding mode for floating-point operations | |||
*<code>FLT_EVAL_METHOD</code> (C99) – evaluation method of expressions involving different floating-point types | |||
*<code>FLT_RADIX</code> – radix of the exponent in the floating-point types | |||
*<code>FLT_DIG</code>, <code>DBL_DIG</code>, <code>LDBL_DIG</code> – number of decimal digits that can be represented without losing precision by {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_EPSILON</code>, <code>DBL_EPSILON</code>, <code>LDBL_EPSILON</code> – [[Machine epsilon|difference between 1.0 and the next representable value]] of {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_MANT_DIG</code>, <code>DBL_MANT_DIG</code>, <code>LDBL_MANT_DIG</code> – number of <code>FLT_RADIX</code>-base digits in the floating-point significand for types {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_MIN_EXP</code>, <code>DBL_MIN_EXP</code>, <code>LDBL_MIN_EXP</code> – minimum negative integer such that <code>FLT_RADIX</code> raised to a power one less than that number is a normalized {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_MIN_10_EXP</code>, <code>DBL_MIN_10_EXP</code>, <code>LDBL_MIN_10_EXP</code> – minimum negative integer such that 10 raised to a power one less than that number is a normalized {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_MAX_EXP</code>, <code>DBL_MAX_EXP</code>, <code>LDBL_MAX_EXP</code> – maximum positive integer such that <code>FLT_RADIX</code> raised to a power one more than that number is a normalized {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>FLT_MAX_10_EXP</code>, <code>DBL_MAX_10_EXP</code>, <code>LDBL_MAX_10_EXP</code> – maximum positive integer such that 10 raised to a power one more than that number is a normalized {{cpp|float}}, {{cpp|double}}, {{cpp|long double}} respectively | |||
*<code>DECIMAL_DIG</code> (C99) – minimum number of decimal digits such that any number of the widest supported floating-point type can be represented in decimal with a precision of <code>DECIMAL_DIG</code> digits and read back in the original floating-point type without changing its value. <code>DECIMAL_DIG</code> is at least 10. | |||
=={{anchor|stdint.h|inttypes.h}}Fixed-width integer types== | |||
The [[C99]] standard includes definitions of several new integer types to enhance the portability of programs.<ref name="c99"/> The already available basic integer types were deemed insufficient, because their actual sizes are implementation defined and may vary across different systems. The new types are especially useful in [[Embedded system|embedded environments]] where hardware supports usually only several types and that support varies from system to system. All new types are defined in <code><inttypes.h></code> header (<code>cinttypes</code> header in C++) and also are available at <code><stdint.h></code> header (<code>cstdint</code> header in C++). The types can be grouped into the following categories: | |||
* Exact-width integer types which are guaranteed to have the same number '''N''' of bits across all implementations. Included only if it is available in the implementation. | |||
* Least-width integer types which are guaranteed to be the smallest type available in the implementation, that has at least specified number '''N''' of bits. Guaranteed to be specified for at least N=8,16,32,64. | |||
* Fastest integer types which are guaranteed to be the fastest integer type available in the implementation, that has at least specified number '''N''' of bits. Guaranteed to be specified for at least N=8,16,32,64. | |||
* Pointer integer types which are guaranteed to be able to hold a pointer | |||
* Maximum-width integer types which are guaranteed to be the largest integer type in the implementation | |||
The following table summarizes the types and the interface to acquire the implementation details ('''N''' refers to the number of bits): | |||
{| class=wikitable | |||
|- | |||
! rowspan=2 | Type category | |||
! colspan=3 | Signed types | |||
! colspan=3 | Unsigned types | |||
|- | |||
! Type | |||
! Minimum value | |||
! Maximum value | |||
! Type | |||
! Minimum value | |||
! Maximum value | |||
|- | |||
! Exact width | |||
| <code>int'''N'''_t</code> || <code>INT'''N'''_MIN</code> || <code>INT'''N'''_MAX</code> | |||
| <code>uint'''N'''_t</code> || 0 || <code>UINT'''N'''_MAX</code> | |||
|- | |||
! Least width | |||
| <code>int_least'''N'''_t</code> || <code>INT_LEAST'''N'''_MIN</code> || <code>INT_LEAST'''N'''_MAX</code> | |||
| <code>uint_least'''N'''_t</code> || 0 || <code>UINT_LEAST'''N'''_MAX</code> | |||
|- | |||
! Fastest | |||
| <code>int_fast'''N'''_t</code> || <code>INT_FAST'''N'''_MIN</code> || <code>INT_FAST'''N'''_MAX</code> | |||
| <code>uint_fast'''N'''_t</code> || 0 || <code>UINT_FAST'''N'''_MAX</code> | |||
|- | |||
! Pointer | |||
| <code>intptr_t</code> || <code>INTPTR_MIN</code> || <code>INTPTR_MAX</code> | |||
| <code>uintptr_t</code> || 0 || <code>UINTPTR_MAX</code> | |||
|- | |||
! Maximum width | |||
| <code>intmax_t</code> || <code>INTMAX_MIN</code> || <code>INTMAX_MAX</code> | |||
| <code>uintmax_t</code> || 0 || <code>UINTMAX_MAX</code> | |||
|} | |||
<!-- | |||
Macros which will convert constant decimal, octal or hexadecimal value which will suit the corresponding type are also defined: | |||
* <code>INTMAX_C(''value'')</code> is substituted for a value suitable for <code>intmax_t</code>. | |||
* <code>UINTMAX_C(''value'')</code> is substituted for a value suitable for <code>uintmax_t</code>.<ref name=pubs /> | |||
==Other integer limits== | |||
* <code>PTRDIFF_MIN</code> is the minimum value of <code>[[Stddef.h#Type ptrdiff_t|ptrdiff_t]]</code>. | |||
* <code>PTRDIFF_MAX</code> is the maximum value of <code>ptrdiff_t</code>. | |||
* <code>SIZE_MAX</code> is the maximum value (2<sup>16</sup> − 1 or greater) of <code>[[Stddef.h#Type size_t|size_t]]</code>. | |||
* <code>WCHAR_MIN</code> is the minimum value of <code>[[Stddef.h#Type wchar_t|wchar_t]]</code>. | |||
* <code>WCHAR_MAX</code> is the maximum value of <code>wchar_t</code>. | |||
* <code>WINT_MIN</code> is the minimum value of <code>wint_t</code>. | |||
* <code>WINT_MAX</code> is the maximum value of <code>wint_t</code>. | |||
* <code>SIG_ATOMIC_MIN</code> is the minimum value of <code>sig_atomic_t</code>. | |||
* <code>SIG_ATOMIC_MAX</code> is the maximum value of <code>sig_atomic_t</code>. | |||
--> | |||
===Printf and scanf format specifiers=== | |||
The <code><inttypes.h></code> header (<code>cinttypes</code> header in C++) provides features that enhance the functionality of the types defined in <code><stdint.h></code> header. Included are macros that define [[printf format string]] and [[scanf format string]] specifiers corresponding to the <code><stdint.h></code> types and several functions for working with <code>intmax_t</code> and <code>uintmax_t</code> types. This header was added in [[C99]]. | |||
;Printf format string | |||
The macros are in the format <code>PRI''{fmt}{type}''</code>. Here ''{fmt}'' defines the output formatting and is one of <code>d</code> (decimal), <code>x</code> (hexadecimal), <code>o</code> (octal), <code>u</code> (unsigned) and <code>i</code> (integer). ''{type}'' defines the type of the argument and is one of <code>'''N'''</code>, <code>FAST'''N'''</code>, <code>LEAST'''N'''</code>, <code>PTR</code>, <code>MAX</code>, where <code>'''N'''</code> corresponds to the number of bits in the argument. | |||
;Scanf format string | |||
The macros are in the format <code>SCN''{fmt}{type}''</code>. Here ''{fmt}'' defines the output formatting and is one of <code>d</code> (decimal), <code>x</code> (hexadecimal), <code>o</code> (octal), <code>u</code> (unsigned) and <code>i</code> (integer). ''{type}'' defines the type of the argument and is one of <code>'''N'''</code>, <code>FAST'''N'''</code>, <code>LEAST'''N'''</code>, <code>PTR</code>, <code>MAX</code>, where <code>'''N'''</code> corresponds to the number of bits in the argument. | |||
;Functions | |||
{{expand section|date=October 2011}} | |||
==Additional floating-point types== | |||
The [[C99]] standard includes new floating-point types <code>float_t</code> and <code>double_t</code>, defined in <code><math.h></code>. They correspond to the types used for the intermediate results of floating-point expressions when <code>FLT_EVAL_METHOD</code> is 0, 1, or 2. These types may be wider than <code>long double</code>. | |||
<!-- This is quite short for a section. Perhaps this could be moved to the "Basic types" one though these are not basic types (just like the new C99 integer types). --> | |||
==Structures== | |||
Structures are a way of storing multiple pieces of data in one variable. For example, say we wanted to store the name and birthday of a person in strings, in one variable. We could use a structure to house that data: | |||
<source lang="c"> | |||
struct birthday | |||
{ | |||
char name[20]; | |||
int day; | |||
int month; | |||
int year; | |||
}; | |||
</source> | |||
Structures may contain pointers to structs of its own type, which is common in [[linked data structure]]s. | |||
A C implementation has freedom to design the memory layout of the struct, with few restrictions; one being that the memory address of the first member will be the same as the address of struct itself. Structs may be [[C syntax#Initialization|initialized]] or assigned to using compound literals. | |||
A user-written function can directly return a structure, though it will often not be very efficient at run-time. | |||
==Arrays== | |||
For every type ''T'', except void and function types, there exist the types “array of ''N'' elements of type ''T''”. | |||
An array is a collection of values, all of the same type, stored contiguously in memory. An array of size ''N'' is indexed by integers from ''0'' up to and including ''N-1''. | |||
There are also "arrays of unspecified size" where the number of elements is not known by the compiler. | |||
For example: | |||
<source lang="c"> | |||
int cat[10]; // array of 10 elements, each of type int | |||
int bob[]; // array of an unspecified number of 'int' elements. | |||
</source> | |||
Arrays can be initialized with a compound initializer, but not assigned. Arrays are passed to functions by passing a pointer to the first element. | |||
Multidimensional arrays are defined as "array of array …". All but the outermost dimension must have compile-time constant size: | |||
<source lang="c"> | |||
int a[10][8]; // array of 10 elements, each of type 'array of 8 int elements' | |||
float f[][32]; // array of unspecified number of 'array of 32 float elements' | |||
</source> | |||
==Pointer types== | |||
For every type ''T'' there exists a type “pointer to ''T''”. | |||
Variables can be declared as being [[pointer (computer programming)|pointers]] to values of various types, by means of the <code>*</code> type declarator. To declare a variable as a pointer, precede its name with an asterisk. | |||
<source lang="c"> | |||
char *square; | |||
long *circle; | |||
</source> | |||
Hence "for every type T" also applies to pointer types there exists multi-indirect pointers like <code>char**</code> or <code>int***</code> and so on. There exists also "pointer to array" types, but they are less common than "array of pointer", and their syntax is quite confusing: | |||
<source lang="c"> | |||
char *pc[10]; // array of 10 elements of 'pointer to char' | |||
char (*pa)[10]; // pointer to a 10-element array of char | |||
</source> | |||
<code>pc</code> consumes 10×<code>sizeof(char*)</code> bytes (usually 40 or 80 bytes on common platforms), but <code>pa</code> is only one pointer, so <code>sizeof(pa)</code> is usually 4 or 8, and the data it refers to is an array of 10 bytes: <code>sizeof(*pa) == 10</code>. | |||
==Unions== | |||
Union types are special structures which allow access to the same memory using different type descriptions; one could, for example, describe a union of data types which would allow reading the same data as an integer, a float or a user declared type: | |||
<source lang="c"> | |||
union | |||
{ | |||
int i; | |||
float f; | |||
struct | |||
{ | |||
unsigned int u; | |||
double d; | |||
} s; | |||
} u; | |||
</source> | |||
In the above example the total size of <code>u</code> is the size of <code>u.s</code> (which happens to be the sum of the sizes of <code>u.s.u</code> and <code>u.s.d</code>), since s is larger than both <code>i</code> and <code>f</code>. When assigning something to <code>u.i</code>, some parts of <code>u.f</code> may be preserved if <code>u.i</code> is smaller than <code>u.f</code>. | |||
Reading from a union member is not the same as casting since the value of the member is not converted, but merely read. | |||
==Function pointers== | |||
Function pointers allow referencing functions with a particular signature. For example, to store the address of the standard function <code>abs</code> in the variable <code>my_int_f</code>: | |||
<source lang="c"> | |||
int (*my_int_f)(int) = &abs; | |||
// the & operator can be omitted, but makes clear that the "address of" abs is used here | |||
</source> | |||
Function pointers are invoked by name just like normal function calls. Function pointers are separate from pointers and [[void pointer]]s. | |||
==See also== | |||
{{wikibooks|C Programming|Variables|C Programming}} | |||
* [[C syntax]] | |||
* [[Uninitialized variable]] | |||
==References== | |||
{{Reflist}} | |||
{{CProLang}} | |||
{{use dmy dates|date=January 2012}} | |||
{{DEFAULTSORT:C Variable Types And Declarations}} | |||
[[Category:C programming language]] | |||
[[Category:C standard library]] |
Revision as of 23:17, 19 December 2013
In the C programming language, data types refers to an extensive system for declaring variables of different types. The language itself provides basic arithmetic types and syntax to build array and compound types. Several headers in the standard library contain definitions of support types, that have additional properties, such as exact size, guaranteed.[1][2]
Basic types
The C language provides many basic types. Most of them are formed from one of the four basic arithmetic type specifiers in C (char
, int
, float
and double
), and optional specifiers (signed
, unsigned
, short
, long
). All available basic arithmetic types are listed below:
Type | Explanation |
---|---|
Template:Cpp | smallest addressable unit of the machine that can contain basic character set. It is an integer type. Actual type can be either signed or unsigned depending on the implementation. |
Template:Cpp | same size as char , but guaranteed to be signed.
|
Template:Cpp | same size as char , but guaranteed to be unsigned.
|
Template:Cpp Template:Cpp Template:Cpp Template:Cpp |
short signed integer type. At least 16 bits in size. |
Template:Cpp Template:Cpp |
same as short , but unsigned.
|
Template:Cpp Template:Cpp |
basic signed integer type. At least 16 bits in size. |
Template:Cpp Template:Cpp |
same as int , but unsigned.
|
Template:Cpp Template:Cpp Template:Cpp Template:Cpp |
long signed integer type. At least 32 bits in size. |
Template:Cpp Template:Cpp |
same as long , but unsigned.
|
Template:Cpp Template:Cpp Template:Cpp Template:Cpp |
long long signed integer type. At least 64 bits in size. Specified since the C99 version of the standard. |
Template:Cpp Template:Cpp |
same as long long , but unsigned. Specified since the C99 version of the standard.
|
Template:Cpp | single precision floating-point type. Actual properties unspecified (except minimum limits), however on most systems this is the IEEE 754 single-precision binary floating-point format. This format is required by the optional Annex F "IEC 60559 floating-point arithmetic". |
Template:Cpp | double precision floating-point type. Actual properties unspecified (except minimum limits), however on most systems this is the IEEE 754 double-precision binary floating-point format. This format is required by the optional Annex F "IEC 60559 floating-point arithmetic". |
Template:Cpp | extended precision floating-point type. Actual properties unspecified. Unlike types Template:Cpp and Template:Cpp, it can be either 80-bit floating point format, the non-IEEE "double-double" or IEEE 754 quadruple-precision floating-point format if a higher precision format is provided, otherwise it is the same as Template:Cpp. See the article on long double for details. |
The actual size of integer types varies by implementation. The standard only requires size relations between the data types and minimum sizes for each data type:
The relation requirements are that the long long
is not smaller than long
, which is not smaller than int
, which is not smaller than short
. As char
's size is always the minimum supported data type, all other data types can't be smaller.
The minimum size for char
is 8 bit, the minimum size for short
and int
is 16 bit, for long
it is 32 bit and long long
must contain at least 64 bit.
The type int
should be the integer type that the target processor is most efficient working with. This allows great flexibility: for example, all types can be 64-bit. However, several different integer width schemes (data models) are popular. This is because the data model defines how different programs communicate, a uniform data model is used within a given operating system application interface.[3]
In practice it should be noted that char
is usually 8 bits in size and short
is usually 16 bits in size (as are their unsigned counterparts). This holds true for platforms as diverse as 1990s SunOS 4 Unix, Microsoft MS-DOS, modern Linux, and Microchip MCC18 for embedded 8 bit PIC microcontrollers. POSIX requires char
to be exactly 8 bits in size.
The actual size and behavior of floating-point types also vary by implementation. The only guarantee is that long double
is not smaller than double
, which is not smaller than float
. Usually, the 32-bit and 64-bit IEEE 754 binary floating-point formats are used, if supported by hardware.
<stdbool.h>...</stdbool.h>
Boolean type
C99 added a boolean (true/false) type (_Bool
) which is defined in the <stdbool.h>
header. Additionally, the standard requires that macros are defined to alias the type as bool
as well as providing macros for true
and false
.
<stddef.h>...</stddef.h>
Size and pointer difference types
The C language provides the separate types size_t
and ptrdiff_t
to represent memory-related quantities. Existing types were deemed insufficient, because their size is defined according to the target processor's arithmetic capabilities, not the memory capabilities, such as available address space. Both of these types are defined in the <stddef.h>
header (cstddef
header in C++).
size_t
is used to represent the size of any object (including arrays) in the particular implementation. It is used as the return type of the sizeof
operator. The maximum size of size_t
is provided via SIZE_MAX
, a macro constant which is defined in the <stdint.h>
header (cstdint
header in C++). It is guaranteed to be at least 65535.
Note that size_t
is unsigned, signed sizes can be represented by ssize_t
.
ptrdiff_t
is used to represent the difference between pointers.
Interface to the properties of the basic types
Information about the actual properties, such as size, of the basic arithmetic types, is provided via macro constants in two headers: <limits.h>
header (climits
header in C++) defines macros for integer types and <float.h>
header (cfloat
header in C++) defines macros for floating-point types. The actual values depend on the implementation.
- Properties of integer types
CHAR_BIT
– size of the Template:Cpp type in bits (at least 8 bits)SCHAR_MIN
,SHRT_MIN
,INT_MIN
,LONG_MIN
,LLONG_MIN
(C99) – minimum possible value of signed integer types: Template:Cpp, Template:Cpp, Template:Cpp, Template:Cpp, Template:CppSCHAR_MAX
,SHRT_MAX
,INT_MAX
,LONG_MAX
,LLONG_MAX
(C99) – maximum possible value of signed integer types: Template:Cpp, Template:Cpp, Template:Cpp, Template:Cpp, Template:CppUCHAR_MAX
,USHRT_MAX
,UINT_MAX
,ULONG_MAX
,ULLONG_MAX
(C99) – maximum possible value of unsigned integer types: Template:Cpp, Template:Cpp, Template:Cpp, Template:Cpp, Template:CppCHAR_MIN
– minimum possible value of Template:CppCHAR_MAX
– maximum possible value of Template:CppMB_LEN_MAX
– maximum number of bytes in a multibyte character
- Properties of floating-point types
FLT_MIN
,DBL_MIN
,LDBL_MIN
– minimum normalized positive value of Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_TRUE_MIN
,DBL_TRUE_MIN
,LDBL_TRUE_MIN
(C11) – minimum positive value of Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_MAX
,DBL_MAX
,LDBL_MAX
– maximum finite value of Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_ROUNDS
– rounding mode for floating-point operationsFLT_EVAL_METHOD
(C99) – evaluation method of expressions involving different floating-point typesFLT_RADIX
– radix of the exponent in the floating-point typesFLT_DIG
,DBL_DIG
,LDBL_DIG
– number of decimal digits that can be represented without losing precision by Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_EPSILON
,DBL_EPSILON
,LDBL_EPSILON
– difference between 1.0 and the next representable value of Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_MANT_DIG
,DBL_MANT_DIG
,LDBL_MANT_DIG
– number ofFLT_RADIX
-base digits in the floating-point significand for types Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_MIN_EXP
,DBL_MIN_EXP
,LDBL_MIN_EXP
– minimum negative integer such thatFLT_RADIX
raised to a power one less than that number is a normalized Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_MIN_10_EXP
,DBL_MIN_10_EXP
,LDBL_MIN_10_EXP
– minimum negative integer such that 10 raised to a power one less than that number is a normalized Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_MAX_EXP
,DBL_MAX_EXP
,LDBL_MAX_EXP
– maximum positive integer such thatFLT_RADIX
raised to a power one more than that number is a normalized Template:Cpp, Template:Cpp, Template:Cpp respectivelyFLT_MAX_10_EXP
,DBL_MAX_10_EXP
,LDBL_MAX_10_EXP
– maximum positive integer such that 10 raised to a power one more than that number is a normalized Template:Cpp, Template:Cpp, Template:Cpp respectivelyDECIMAL_DIG
(C99) – minimum number of decimal digits such that any number of the widest supported floating-point type can be represented in decimal with a precision ofDECIMAL_DIG
digits and read back in the original floating-point type without changing its value.DECIMAL_DIG
is at least 10.
Fixed-width integer types
The C99 standard includes definitions of several new integer types to enhance the portability of programs.[2] The already available basic integer types were deemed insufficient, because their actual sizes are implementation defined and may vary across different systems. The new types are especially useful in embedded environments where hardware supports usually only several types and that support varies from system to system. All new types are defined in <inttypes.h>
header (cinttypes
header in C++) and also are available at <stdint.h>
header (cstdint
header in C++). The types can be grouped into the following categories:
- Exact-width integer types which are guaranteed to have the same number N of bits across all implementations. Included only if it is available in the implementation.
- Least-width integer types which are guaranteed to be the smallest type available in the implementation, that has at least specified number N of bits. Guaranteed to be specified for at least N=8,16,32,64.
- Fastest integer types which are guaranteed to be the fastest integer type available in the implementation, that has at least specified number N of bits. Guaranteed to be specified for at least N=8,16,32,64.
- Pointer integer types which are guaranteed to be able to hold a pointer
- Maximum-width integer types which are guaranteed to be the largest integer type in the implementation
The following table summarizes the types and the interface to acquire the implementation details (N refers to the number of bits):
Type category | Signed types | Unsigned types | ||||
---|---|---|---|---|---|---|
Type | Minimum value | Maximum value | Type | Minimum value | Maximum value | |
Exact width | intN_t |
INTN_MIN |
INTN_MAX
|
uintN_t |
0 | UINTN_MAX
|
Least width | int_leastN_t |
INT_LEASTN_MIN |
INT_LEASTN_MAX
|
uint_leastN_t |
0 | UINT_LEASTN_MAX
|
Fastest | int_fastN_t |
INT_FASTN_MIN |
INT_FASTN_MAX
|
uint_fastN_t |
0 | UINT_FASTN_MAX
|
Pointer | intptr_t |
INTPTR_MIN |
INTPTR_MAX
|
uintptr_t |
0 | UINTPTR_MAX
|
Maximum width | intmax_t |
INTMAX_MIN |
INTMAX_MAX
|
uintmax_t |
0 | UINTMAX_MAX
|
Printf and scanf format specifiers
The <inttypes.h>
header (cinttypes
header in C++) provides features that enhance the functionality of the types defined in <stdint.h>
header. Included are macros that define printf format string and scanf format string specifiers corresponding to the <stdint.h>
types and several functions for working with intmax_t
and uintmax_t
types. This header was added in C99.
- Printf format string
The macros are in the format PRI{fmt}{type}
. Here {fmt} defines the output formatting and is one of d
(decimal), x
(hexadecimal), o
(octal), u
(unsigned) and i
(integer). {type} defines the type of the argument and is one of N
, FASTN
, LEASTN
, PTR
, MAX
, where N
corresponds to the number of bits in the argument.
- Scanf format string
The macros are in the format SCN{fmt}{type}
. Here {fmt} defines the output formatting and is one of d
(decimal), x
(hexadecimal), o
(octal), u
(unsigned) and i
(integer). {type} defines the type of the argument and is one of N
, FASTN
, LEASTN
, PTR
, MAX
, where N
corresponds to the number of bits in the argument.
- Functions
Additional floating-point types
The C99 standard includes new floating-point types float_t
and double_t
, defined in <math.h>
. They correspond to the types used for the intermediate results of floating-point expressions when FLT_EVAL_METHOD
is 0, 1, or 2. These types may be wider than long double
.
Structures
Structures are a way of storing multiple pieces of data in one variable. For example, say we wanted to store the name and birthday of a person in strings, in one variable. We could use a structure to house that data:
struct birthday
{
char name[20];
int day;
int month;
int year;
};
Structures may contain pointers to structs of its own type, which is common in linked data structures.
A C implementation has freedom to design the memory layout of the struct, with few restrictions; one being that the memory address of the first member will be the same as the address of struct itself. Structs may be initialized or assigned to using compound literals.
A user-written function can directly return a structure, though it will often not be very efficient at run-time.
Arrays
For every type T, except void and function types, there exist the types “array of N elements of type T”.
An array is a collection of values, all of the same type, stored contiguously in memory. An array of size N is indexed by integers from 0 up to and including N-1.
There are also "arrays of unspecified size" where the number of elements is not known by the compiler.
For example:
int cat[10]; // array of 10 elements, each of type int
int bob[]; // array of an unspecified number of 'int' elements.
Arrays can be initialized with a compound initializer, but not assigned. Arrays are passed to functions by passing a pointer to the first element.
Multidimensional arrays are defined as "array of array …". All but the outermost dimension must have compile-time constant size:
int a[10][8]; // array of 10 elements, each of type 'array of 8 int elements'
float f[][32]; // array of unspecified number of 'array of 32 float elements'
Pointer types
For every type T there exists a type “pointer to T”.
Variables can be declared as being pointers to values of various types, by means of the *
type declarator. To declare a variable as a pointer, precede its name with an asterisk.
char *square;
long *circle;
Hence "for every type T" also applies to pointer types there exists multi-indirect pointers like char**
or int***
and so on. There exists also "pointer to array" types, but they are less common than "array of pointer", and their syntax is quite confusing:
char *pc[10]; // array of 10 elements of 'pointer to char'
char (*pa)[10]; // pointer to a 10-element array of char
pc
consumes 10×sizeof(char*)
bytes (usually 40 or 80 bytes on common platforms), but pa
is only one pointer, so sizeof(pa)
is usually 4 or 8, and the data it refers to is an array of 10 bytes: sizeof(*pa) == 10
.
Unions
Union types are special structures which allow access to the same memory using different type descriptions; one could, for example, describe a union of data types which would allow reading the same data as an integer, a float or a user declared type:
union
{
int i;
float f;
struct
{
unsigned int u;
double d;
} s;
} u;
In the above example the total size of u
is the size of u.s
(which happens to be the sum of the sizes of u.s.u
and u.s.d
), since s is larger than both i
and f
. When assigning something to u.i
, some parts of u.f
may be preserved if u.i
is smaller than u.f
.
Reading from a union member is not the same as casting since the value of the member is not converted, but merely read.
Function pointers
Function pointers allow referencing functions with a particular signature. For example, to store the address of the standard function abs
in the variable my_int_f
:
int (*my_int_f)(int) = &abs;
// the & operator can be omitted, but makes clear that the "address of" abs is used here
Function pointers are invoked by name just like normal function calls. Function pointers are separate from pointers and void pointers.
See also
DTZ's auction group in Singapore auctions all types of residential, workplace and retail properties, retailers, homes, accommodations, boarding houses, industrial buildings and development websites. Auctions are at the moment held as soon as a month.
Whitehaven @ Pasir Panjang – A boutique improvement nicely nestled peacefully in serene Pasir Panjang personal estate presenting a hundred and twenty rare freehold private apartments tastefully designed by the famend Ong & Ong Architect. Only a short drive away from Science Park and NUS Campus, Jade Residences, a recent Freehold condominium which offers high quality lifestyle with wonderful facilities and conveniences proper at its door steps. Its fashionable linear architectural fashion promotes peace and tranquility living nestled within the D19 personal housing enclave. Rising workplace sector leads real estate market efficiency, while prime retail and enterprise park segments moderate and residential sector continues in decline International Market Perspectives - 1st Quarter 2014
There are a lot of websites out there stating to be one of the best seek for propertycondominiumhouse, and likewise some ways to discover a low cost propertycondominiumhouse. Owning a propertycondominiumhouse in Singapore is the dream of virtually all individuals in Singapore, It is likely one of the large choice we make in a lifetime. Even if you happen to're new to Property listing singapore funding, we are right here that will help you in making the best resolution to purchase a propertycondominiumhouse at the least expensive value.
Jun 18 ROCHESTER in MIXED USE IMPROVEMENT $1338000 / 1br - 861ft² - (THE ROCHESTER CLOSE TO NORTH BUONA VISTA RD) pic real property - by broker Jun 18 MIXED USE IMPROVEMENT @ ROCHESTER @ ROCHESTER PK $1880000 / 1br - 1281ft² - (ROCHESTER CLOSE TO NORTH BUONA VISTA) pic real estate - by broker Tue 17 Jun Jun 17 Sunny Artwork Deco Gem Near Seashore-Super Deal!!! $103600 / 2br - 980ft² - (Ventnor) pic actual estate - by owner Jun 17 Freehold semi-d for rent (Jalan Rebana ) $7000000 / 5909ft² - (Jalan Rebana ) actual property - by dealer Jun sixteen Ascent @ 456 in D12 (456 Balestier Highway,Singapore) pic real property - by proprietor Jun 16 RETAIL SHOP AT SIM LIM SQUARE FOR SALE, IT MALL, ROCHOR, BUGIS MRT $2000000 / 506ft² - (ROCHOR, BUGIS MRT) pic real estate - by dealer HDB Scheme Any DBSS BTO
In case you are eligible to purchase landed houses (open solely to Singapore residents) it is without doubt one of the best property investment choices. Landed housing varieties solely a small fraction of available residential property in Singapore, due to shortage of land right here. In the long term it should hold its worth and appreciate as the supply is small. In truth, landed housing costs have risen the most, having doubled within the last eight years or so. However he got here back the following day with two suitcases full of money. Typically we've got to clarify to such folks that there are rules and paperwork in Singapore and you can't just buy a home like that,' she said. For conveyancing matters there shall be a recommendedLondon Regulation agency familiar with Singapore London propertyinvestors to symbolize you
Sales transaction volumes have been expected to hit four,000 units for 2012, close to the mixed EC gross sales volume in 2010 and 2011, in accordance with Savills Singapore. Nevertheless the last quarter was weak. In Q4 2012, sales transactions were 22.8% down q-q to 7,931 units, in line with the URA. The quarterly sales discount was felt throughout the board. When the sale just starts, I am not in a hurry to buy. It's completely different from a private sale open for privileged clients for one day solely. Orchard / Holland (D09-10) House For Sale The Tembusu is a singular large freehold land outdoors the central area. Designed by multiple award-profitable architects Arc Studio Architecture + Urbanism, the event is targeted for launch in mid 2013. Post your Property Condos Close to MRT
References
43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.
30 year-old Entertainer or Range Artist Wesley from Drumheller, really loves vehicle, property developers properties for sale in singapore singapore and horse racing. Finds inspiration by traveling to Works of Antoni Gaudí.
- ↑ Template:Cite web
- ↑ 2.0 2.1 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 - ↑ Template:Cite web