Integer Types
Common integer types
C++ supports several integer types with varying sizes and ranges. Here is a list of the most commonly used integer types in C++, available since the earlier versions of the language. Note that char is treated as integer type here for practical reason, though technically it is not.
| Type name | Typical Size (in bytes) | Range |
|---|---|---|
bool | 1 | Boolean literal true or false, added in C++98 |
char | 1 | [-128, 127] or [0, 255] depending on signedness |
short | 2 | [-32,768, 32,767] |
int | 4 | [-2,147,483,648, 2,147,483,647] |
long | 4 or 8 | [-2,147,483,648, 2,147,483,647] or [-9,223,372,036,854,775,808, 9,223,372,036,854,775,807] depending on platform |
long long | 8 | [-9,223,372,036,854,775,808, 9,223,372,036,854,775,807] |
unsigned char | 1 | [0, 255] |
unsigned short | 2 | [0, 65,535] |
unsigned int | 4 | [0, 4,294,967,295] |
unsigned long | 4 or 8 | [0, 4,294,967,295] or [0, 18,446,744,073,709,551,615] depending on platform |
unsigned long long | 8 | [0, 18,446,744,073,709,551,615] |
The C++ standard does not specify the minimum bytes for these integer types, except the following constraints:
sizeof(char) == 1 // Rule 1
sizeof(char) <= sizeof(short) // Rule 2
sizeof(short) <= sizeof(int) // Rule 3
sizeof(int) <= sizeof(long) // Rule 4
sizeof(long) <= sizeof(long long) // Rule 5
sizeof(char) * CHAR_BIT >= 8 // Rule 6
sizeof(short) * CHAR_BIT >= 16 // Rule 7
sizeof(int) * CHAR_BIT >= 16 // Rule 8
sizeof(long) * CHAR_BIT >= 32 // Rule 9
sizeof(long long) * CHAR_BIT >= 64 // Rule 10
CHAR_BIT represents the number of bits in a char type. Although most modern architectures use 8 bits per byte, this is not always the case as some older machines may have used 7-bit bytes. Under Rule 4, C/C++ allows long and int to have the same size, but it must be at least 32 bits according to Rule 9.
Fixed size integer types
The C++11 standard introduced new integer types such as int8_t, int16_t, int32_t, and int64_t with fixed sizes, as well as their unsigned counterparts, uint8_t, uint16_t, uint32_t, and uint64_t. These types are guaranteed to have the specified size and range on any conforming implementation.
The following table summarizes fixed size integer types - note that the intN_t and uintN_t types are guaranteed to have exactly N bits, where N is 8, 16, 32, or 64.
| Type | Size (in bytes) | Range |
|---|---|---|
int8_t | 1 | [-128, 127] |
uint8_t | 1 | [0, 255] |
int16_t | 2 | [-32,768, 32,767] |
uint16_t | 2 | [0, 65,535] |
int32_t | 4 | [-2,147,483,648, 2,147,483,647] |
uint32_t | 4 | [0, 4,294,967,295] |
int64_t | 8 | [-9,223,372,036,854,775,808, 9,223,372,036,854,775,807] |
uint64_t | 8 | [0, 18,446,744,073,709,551,615] |
128-bit integer types
The C++ standard does not define a 128-bit integer type, as of the latest version C++20.
However, some compilers and libraries provide extensions that define a 128-bit integer type. For example, the GCC and Clang compilers provide an __int128 type, which is a 128-bit signed integer type. The Boost Multiprecision library provides several integer types with arbitrary precision, including a boost::multiprecision::int128_t type.
| Type name | Library/Compiler | Description |
|---|---|---|
__int128 | GCC, Clang | A 128-bit signed integer type |
unsigned __int128 | GCC, Clang | A 128-bit unsigned integer type |
int128_t | Boost Multiprecision | A 128-bit signed integer type |
uint128_t | Boost Multiprecision | A 128-bit unsigned integer type |
It's important to note that the availability and behavior of non-standard integer types may vary depending on the platform and compiler used.