C++ integer types a tutorial !
The integer types in C++ are fundamental types. A fundamental type , has a mapping to hardware , so the operations performed on a fundamental type , are hardware performed .
Boolean , Characters , and integer types , are called the integral types. The integral types and the floating point types are called the arithmetic types .
What are the C++ integer types
An integer type is a whole number, as in -1or 1. A whole number does not contain a fractional part , such as .2.
Integer types can either be unsigned or signed . An unsigned integer , can only be non negative , for example 0, or 1, whereas a signed integer , can be negative , positive , or zero , as in -1, or 3.
C++ standards , prior to C++20 , do not specify the algorithm for representing the signed , or unsigned integer types . A signed integer , can be represented , using one’s complements , two’s complement , or sign and magnitude . C++20 , specifies that signed integers , must be represented using two’s complement .
The C++ standards dictates that unsigned arithmetic , such as addition , or subtraction , must obey arithmetic modulo two , to the power n, this is related to overflow . Overflow happens , when the result is too large to fit in the allocated width , for an integer type .
An integer type , can have multiple type specifiers, for example : int, signed int, and signed, represent the same integer type int, which is signed . This being said , an integer type can be declared in multiple ways , or using multiple keywords.
short int , short
unsigned short int , unsigned short
int , signed , signed int
unsigned int , unsigned
long int , signed long int , signed long
unsigned long int , unsigned long ,
long long int , signed long long int, signed long long , long long
unsigned long long int , unsigned long longIt is clear , from the preceding list , that for signed integer types , it is not necessary to use the keyword signed.
A signed integer type , and its unsigned version , such as int, and unsigned int, have the same storage size and alignment . Alignment is where in memory , an object can be placed .
An implementation can define other integer types, called the extended integer types . For each extended integer type , a signed , and an unsigned version , must be defined .
What are the C++ integer types ranges
The C++ standard specifies the minimum ranges, that a signed or an unsigned integer type , might have , an implementation , can define larger ranges .
Before C++ 20 , and because signed integer types could have , a sign and magnitude representation , the minimum ranges were :
Starting C++20 , the minimum ranges are :
The minimum ranges of the integral types , as implemented on a given machine , are defined by the C++ header climits.
#include<iostream>
#include<climits>int main(void ){
using std::cout;
using std::endl; cout << "CHAR_BIT : " << CHAR_BIT << endl;
/*Print the number of bits in a char .*/ cout << "SCHAR_MIN : " << SCHAR_MIN << endl;
/*Print the minimum value of signed char .*/ cout << "SCHAR_MAX : " << SCHAR_MAX << endl;
/*Print the maximum value of signed char .*/ cout << "UCHAR_MAX : " << UCHAR_MAX << endl;
/*Print the maximum value of unsigned char .*/ cout << "CHAR_MIN : " << CHAR_MIN << endl;
/*Print the minimum value of char .*/ cout << "CHAR_MAX : " << CHAR_MAX << endl;
/*Print the maximum value of char .*/ cout << "MB_LEN_MAX : " << MB_LEN_MAX << endl;
/*Print maximum number of bytes available in
a multibyte character .*/ cout << "SHRT_MIN : " << SHRT_MIN << endl;
/*Print the minimum value of short .*/ cout << "SHRT_MAX : " << SHRT_MAX << endl;
/*Print the maximum value of short .*/ cout << "USHRT_MAX : " << USHRT_MAX << endl;
/*Print the minimum value of unsigned short .*/ cout << "INT_MIN : " << INT_MIN << endl;
/*Print the minimum value of int .*/ cout << "INT_MAX : " << INT_MAX << endl;
/*Print the maximum value of int .*/ cout << "UINT_MAX : " << UINT_MAX << endl;
/*Print the maximum value of unsigned int .*/ cout << "LONG_MIN : " << LONG_MIN << endl;
/*Print the minimum value of long .*/ cout << "LONG_MAX : " << LONG_MAX << endl;
/*Print the maximum value of long .*/ cout << "ULONG_MAX : " << ULONG_MAX << endl;
/*Print the maximum value of unsigned long .*/ cout << "LLONG_MIN : " << LLONG_MIN << endl;
/*Print the minimum value of long long .*/ cout << "LLONG_MAX : " << LLONG_MAX << endl;
/*Print the maximum value of long long .*/ cout << "ULLONG_MAX : " << ULLONG_MAX << endl;
/*Print the maximum value of unsigned long long .*/ }/*Output
CHAR_BIT : 8
SCHAR_MIN : -128
SCHAR_MAX : 127
UCHAR_MAX : 255
CHAR_MIN : -128
CHAR_MAX : 127
MB_LEN_MAX : 6
SHRT_MIN : -32768
SHRT_MAX : 32767
USHRT_MAX : 65535
INT_MIN : -2147483648
INT_MAX : 2147483647
UINT_MAX : 4294967295
LONG_MIN : -9223372036854775808
LONG_MAX : 9223372036854775807
ULONG_MAX : 18446744073709551615
LLONG_MIN : -9223372036854775808
LLONG_MAX : 9223372036854775807
ULLONG_MAX : 18446744073709551615 */
The sizeof operator , returns the number of bytes, which are reserved for a given type , hence it can be used to get the number of bytes , reserved for integer types .
#include<iostream>int main(void ){
using std::cout;
using std::endl; cout << sizeof(short ) << endl;
//Output on this machine : 2 cout << sizeof(int ) << endl;
//Output on this machine : 4 cout << sizeof(long ) << endl ;
//Output on this machine : 8 cout << sizeof(long long ) << endl;
/*Output on this machine : 8 */ }
C++ integer literals types
An integer literal such as 17, can be written in base 2, 8, 10, or 16, as follows :
#include<iostream>int main(void ){
using std::cout;
using std::endl; cout << "17 in binary is : " << 0b1'00'01 << endl;
/*Binary literals start by 0B , case insensitive ,
a single quote can be use in any integer
literal for readability .*/ cout << "17 in octal is : " << 021 << endl;
/*Octal literals start by 0 .*/ cout << "17 in hexadecimal is : " << 0x11 << endl;
/*Hexadecimal literals start by
0X , case insensitive .*/ cout << "17 in decimal is : " << 17 << endl;
/*Decimal literals must not start by
0 .*//*Output :
17 in binary is : 17
17 in octal is : 17
17 in hexadecimal is : 17
17 in decimal is : 17 */ }
Since C++ is a typed language , an integer literal has a type. An integer literal is always non negative , the negation operator -, is applied on the gotten integer literal type .
Decimal integer literals , have a default type ofint, if too large to fit in an int, they will have a long type , if too large to fit in a long, they will have the long longtype . If still too large to fit , and the implementation defines extended integer types , they are tried , as described , if still too large , the behavior is implementation defined .
Binary , octal , and hexadecimal integer literals , have a default type ofint, if too large to fit in an int, they will have a type of unsigned int, if too large to fit in an unsigned int, they will have a type of long, next unsigned long, next long long, next unsigned long long, next if the implementation defines extended integer types , they are tried as stated , if still too large , the behavior is implementation defined .
#include<iostream>int main(void ){
using std::cout;
using std::endl; unsigned int var_i = -2147483648;
/*int on this machine has a range of
[-2147483648 , 2147483647 ] .
2147483648 is larger than INT_MAX ,
2147483648 is a decimal integer literal ,
hence long int is tried .
long int on this machine has a range of
[-9223372036854775808 , 9223372036854775807 ]
, hence 2147483648 is of type long int .
The negation operator is applied on
2147483648 , as such -2147483648 , is gotten .
var_i is an unsigned int , and the gotten
value is a long . Hence the gotten value
is converted first to unsigned long , bits
are kept as is , just reinterpreted , so
the converted value is 2147483648 in
unsigned long , next the converted value
is truncated to an unsigned int , the value
is preserved in truncation . */ cout << var_i << endl ;
/*Output :
2147483648 .*/ var_i = -0x80000000;
/*0x80000000 in hexadecimal is equal to
2147483648 in decimal .
First int is tried .
On this machine it has a range of
[-2147483648 , 2147483647 ] , next
unsigned int is tried .
On this machine , unsigned int has
a range of [0 , 4294967295 ] ,
hence 0x80000000 is of type unsigned
int .
The negation operator is applied ,
modulo 4294967296 is applied , and the
result is 2147483648 .*/ cout << var_i << endl ;
/*Output :
2147483648 .*/ }
The suffixes l, and ll, case insensitive , can be used with an integer literal , to state that it is of type long, or long long. In such cases , and to determine the type of the integer literal , the compiler starts from long, or long long, depending on the suffix , and try the next types , as described earlier .
The suffix u, case insensitive , can be applied to an integer literal , to state that it is unsigned . In such case , unsigned intis first tried , followed by unsigned long, followed by unsigned long long. If still too large , and the implementation defines extended integer types , the extended integer types are tried , as stated , if still too large , the behavior is implementation defined .
The suffix ucan be used with the suffixes l, and llto state that an integer literal is unsigned long, or unsigned long long. In such a case , the compiler tries , the next larger unsigned type , if the literal is too large to fit ,and if no unsigned integer type can fit the literal , then the behavior is implementation defined .
#include<iostream>int main(void ){
using std::cout;
using std::endl; int var_i = 2147483648u;
/*The suffix u is used , as such
the integer literal 2147483648
is of an unsigned integer type .
unsigned int , on this machine
has a range of [0 , 4294967295 ]
, 2147483648 can fit in this range ,
so 2147483648 is of type unsigned int .
var_i is a signed int , as such the
gotten unsigned value , is reinterpreted
as being signed .*/ cout << var_i << endl ;
/*Output
-2147483648 */ var_i = 9223372036854775807L ;
/*9223372036854775807 is suffixed with
L , as such long is first tried .
Long on this machine , has a range
[-9223372036854775808 , 9223372036854775807 ] .
It can hold 9223372036854775807 , so the
integer literal is of type long .
var_i is of type int , as such ,
the gotten long value is truncated ,
and the result is -1 .*/ cout << var_i << endl ;
/*Output :
-1 */ auto var_ul = 1lu;
/*The integer literal 1 , is suffixed
with lu , so it is of the unsigned long
type .
auto is used , as not to write the
type of var_ul , since the integer
literal is of type unsigned long , hence
var_ul , is of type unsigned long .
ul could have been used instead of lu .*/ }
C++ Standard library integer types
The integer types defined by the C++ standard , are defined to have a least width , as such a least range , so the range of a standard integer type , is not uniform across all implementations .
For example, on a 16bit architecture , inthave typically a width of 16bits , whereas on a 32bits architecture , inthas typically a width of 32bits .
The question to ask is as such , what if what was needed , is to have a fixed length width , for an integer type , across all implementations ?
Thestandard library header cstdint, defines fixed width integer types, they are :
int8_t
uint8_t
/*Fixed width 8 bits signed and
unsigned integers .*/int16_t
uint16_t
/*Fixed width 16 bits signed and
unsigned integers .*/int32_t
uint32_t
/*Fixed width 32 bits signed and
unsigned integers .*/int64_t
uint64_t
/*Fixed width 64 bits signed and
unsigned integers .*/
The fixed width integer types , are optional, so it is not necessary for an implementation to provide them .
What about , if what was needed , is an integer type , for which a processor in an execution environment , so where the program is being executed , is faster to perform operations, and this integer type , is to be of a minimum length ? The standard library cstdintheader , defines the following integer types , that fit these requirements :
int_fast8_t
uint_fast8_t
/*Fastest , signed , unsigned integer
types , that have at least 8 bits .*/int_fast16_t
uint_fast6_t
/*Fastest , signed , unsigned integer
types , that have at least 16 bits .*/int_fast32_t
uint_fast32_t
/*Fastest , signed , unsigned integer
types , that have at least 32 bits .*/int_fast64_t
uint_fast64_t
/*Fastest , signed , unsigned integer
types , that have at least 64 bits .*/
Finally what if what was needed , is to have the largest integer type , available on an implementation . To fulfill , this requirement , the cstdintheader defines :
intmax_t
uintmax_t
/*widest signed , unsigned , integer types
available on an implementation .*/Originally published at https://twiserandom.com on February 22, 2021.
