浅析uint8_t / uint16_t / uint32_t /uint64_t

简单来说，uint8_t / uint16_t / uint32_t /uint64_t这些数据类型都只是别名而来，具体如下：

一、C语言数据基本类型

在C语言中有6种基本数据类型：short、int、long、float、double、char

1）整型：short  int、int、long int

2）浮点型：float、double

3）字符类型：char

---

二、分析uint8_t\uint_16_t\uint32_t\uint64_t

1、数据来源：这些数据类型中都带有_t, _t 表示这些数据类型是通过typedef定义的，而不是新的数据类型。也就是说，它们其实是我们已知的类型的别名。

2、typedef：typedef用来定义关键字或标识符的别名

3、使用原因：方便代码的维护。比如，在C中没有bool型，于是在一个软件中，一个程序员使用int，一个程序员使用short，会比较混乱，最好用一个typedef来定义一个统一的bool，每个程序员都可以用这个别名的bool。

不同的平台会有不同的字长，所以利用预编译和typedef可以方便的维护代码。

typedef unsigned char uint8_t;//将uint8_t别名为无符号字符型

4、定义：在C99标准中定义了这些数据类型，具体定义在：stdint.h中

定义类型如下：

typedef   signed          char int8_t;
typedef   signed short     int int16_t;
typedef   signed           int int32_t;
typedef   signed       __INT64 int64_t;

/* exact-width unsigned integer types */
typedef unsigned          char uint8_t;
typedef unsigned short     int uint16_t;
typedef unsigned           int uint32_t;
typedef unsigned       __INT64 uint64_t;

/* 7.18.1.2 */
/* smallest type of at least n bits */
/* minimum-width signed integer types */
typedef   signed          char int_least8_t;
typedef   signed short     int int_least16_t;
typedef   signed           int int_least32_t;
typedef   signed       __INT64 int_least64_t;

/* minimum-width unsigned integer types */
typedef unsigned          char uint_least8_t;
typedef unsigned short     int uint_least16_t;
typedef unsigned           int uint_least32_t;
typedef unsigned       __INT64 uint_least64_t;

/* 7.18.1.3 */
/* fastest minimum-width signed integer types */
typedef   signed           int int_fast8_t;
typedef   signed           int int_fast16_t;
typedef   signed           int int_fast32_t;
typedef   signed       __INT64 int_fast64_t;

/* fastest minimum-width unsigned integer types */
typedef unsigned           int uint_fast8_t;
typedef unsigned           int uint_fast16_t;
typedef unsigned           int uint_fast32_t;
typedef unsigned       __INT64 uint_fast64_t;

/* 7.18.1.4 integer types capable of holding object pointers */
#if __sizeof_ptr == 8
typedef   signed       __INT64 intptr_t;
typedef unsigned       __INT64 uintptr_t;
#else
typedef   signed           int intptr_t;
typedef unsigned           int uintptr_t;
#endif

/* 7.18.1.5 greatest-width integer types */
typedef   signed     __LONGLONG intmax_t;
typedef unsigned     __LONGLONG uintmax_t;

5、格式化输出：

1）uint16_t %hu

2）uint32_t %u

3）uint64_t %llu

6、uint8_t类型的输出：

typedef unsigned char uint8_t;//将uint8_t别名为无符号字符型

uint8_t buf = 65;

printf("buf = %d",buf);//错误
printf("buf = %c",buf);//正确，打印出字符的ASCII码