Fixed width integer types (since C++11)

type and range

越界问题非常频繁地困扰着开发人员

CPP常用的类型定义不能体现数据的bit位数，让开发人员非常抓狂，相信很多人都遇到过，当判定一个数值是否越界时候，一定是先去网上查表，

但是数据类型对应的范围，依赖具体的compiler的编译器实现的， 嵌入式系统往往范围比较小， 服务器系统编译范围一般按照如下标准的来。

 

https://www.geeksforgeeks.org/c-data-types/

Data Type	Size (in bytes)	Range
short int	2	-32,768 to 32,767
unsigned short int	2	0 to 65,535
unsigned int	4	0 to 4,294,967,295
int	4	-2,147,483,648 to 2,147,483,647
long int	4	-2,147,483,648 to 2,147,483,647
unsigned long int	4	0 to 4,294,967,295
long long int	8	-(2^63) to (2^63)-1
unsigned long long int	8	0 to 18,446,744,073,709,551,615
signed char	1	-128 to 127
unsigned char	1	0 to 255
float	4
double	8
long double	12
wchar_t	2 or 4	1 wide character

 

Note : Above values may vary from compiler to compiler. In the above example, we have considered GCC 32 bit.

 

 

与系统架构也产生迷惑

https://stackoverflow.com/questions/17489857/why-is-int-typically-32-bit-on-64-bit-compilers

Why is int typically 32 bit on 64 bit compilers? When I was starting programming, I've been taught int is typically the same width as the underlying architecture. And I agree that this also makes sense, I find it logical for a unspecified width integer to be as wide as the underlying platform (unless we are talking 8 or 16 bit machines, where such a small range for int will be barely applicable).

 

Later on I learned int is typically 32 bit on most 64 bit platforms. So I wonder what is the reason for this. For storing data I would prefer an explicitly specified width of the data type, so this leaves generic usage for int, which doesn't offer any performance advantages, at least on my system I have the same performance for 32 and 64 bit integers. So that leaves the binary memory footprint, which would be slightly reduced, although not by a lot...

 

这种设计跟与历史折中的相关。

The history, trade-offs and decisions are explained by The Open Group at http://www.unix.org/whitepapers/64bit.html. It covers the various data models, their strengths and weaknesses and the changes made to the Unix specifications to accommodate 64-bit computing.

 

Fixed width integer types

C11标准提出解决办法。

引入新的数据类型， 这种数据类型中添加bit位。

例如 int64_t

这种设计符合设计模式，见名知意。

https://en.cppreference.com/w/cpp/types/integer

Types

Defined in header <cstdint>
int8_tint16_tint32_tint64_t (optional)	signed integer type with width of exactly 8, 16, 32 and 64 bits respectively with no padding bits and using 2's complement for negative values (provided if and only if the implementation directly supports the type) (typedef)
int_fast8_tint_fast16_tint_fast32_tint_fast64_t	fastest signed integer type with width of at least 8, 16, 32 and 64 bits respectively (typedef)
int_least8_tint_least16_tint_least32_tint_least64_t	smallest signed integer type with width of at least 8, 16, 32 and 64 bits respectively (typedef)
intmax_t	maximum-width signed integer type (typedef)
intptr_t (optional)	signed integer type capable of holding a pointer to void (typedef)
uint8_tuint16_tuint32_tuint64_t (optional)	unsigned integer type with width of exactly 8, 16, 32 and 64 bits respectively (provided if and only if the implementation directly supports the type) (typedef)
uint_fast8_tuint_fast16_tuint_fast32_tuint_fast64_t	fastest unsigned integer type with width of at least 8, 16, 32 and 64 bits respectively (typedef)
uint_least8_tuint_least16_tuint_least32_tuint_least64_t	smallest unsigned integer type with width of at least 8, 16, 32 and 64 bits respectively (typedef)
uintmax_t	maximum-width unsigned integer type (typedef)
uintptr_t (optional)	unsigned integer type capable of holding a pointer to void