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将uint8_t 转化为unsigned 类型
使用一元运算符+(和- 运算符对应)
测试代码如下
#include#include #include int main() { std::uint8_t uint8_num = 10; std::cout << "uint8_t num is " << uint8_num << std::endl; //无法打印 std::cout << "after cast to unsigned, uint8_t num is " << unsigned(uint8_num) << std::endl; //能正常打印 std::cout << "with a unary + operator, uint8_t num is " << +uint8_num << std::endl; //能正常打印 std::cout << "type of '+uint8_num' is " << typeid(+uint8_num).name() << std::endl; return 0; }
运行结果如下
可见使用+运算符的原理也是进行类型转换(把uint8_t 转为 int)
补充知识：C 语言printf打印各种数据类型的方法(u8/s8/u16/s16.../u64/double/float)(全)
首先必须知道u8,s8等数据类型的定义：
typedef signed char s8; typedef unsigned char u8; typedef signed short s16; typedef unsigned short u16; typedef signed int s32; typedef unsigned int u32; typedef signed long long s64; typedef unsigned long long u64;
与体系结构相关的，定义在include/linux/type.h文件中：
/* bsd */ typedef unsigned char u_char; typedef unsigned short u_short; typedef unsigned int u_int; typedef unsigned long u_long; /* sysv */ typedef unsigned char unchar; typedef unsigned short ushort; typedef unsigned int uint; typedef unsigned long ulong; #ifndef __BIT_TYPES_DEFINED__ #define __BIT_TYPES_DEFINED__ typedef __u8 u_int8_t; typedef __s8 int8_t; typedef __u16 u_int16_t; typedef __s16 int16_t; typedef __u32 u_int32_t; typedef __s32 int32_t; #endif /* !(__BIT_TYPES_DEFINED__) */ typedef __u8 uint8_t; typedef __u16 uint16_t; typedef __u32 uint32_t; #if defined(__GNUC__) typedef __u64 uint64_t; typedef __u64 u_int64_t; typedef __s64 int64_t;
对于各种数据类型的打印方式总结如下如下：
| 数据类型 | 打印格式 |
|---|---|
| u8 | %d |
| s8 | %d |
| u16 | %d or %hu |
| s16 | %d or %hd |
| u32 | %u |
| s32 | %d |
| u64 | %llu |
| s64 | %lld |
| int | %d |
| unsigned int | %u |
| short int | %d or %hd |
| long | %ld |
| unsigned long | %lu |
| long long | %lld |
| unsigned long long | %llu |
| char | %c |
| char * | %s |
| bool (#define stdbool.h) | %d |
| unsigned int/int------>十六进制 | %0x |
| unsigned long/long---->十六进制 | %0lx |
| long long/unsigned long long ----->十六进制 | %0llx |
| unsigned int/int------>八进制 | %0o |
| unsigned long/long---->八进制 | %0lo |
| long long/unsigned long long ----->八进制 | %0llo |
| float | %f |
| double | %f or %lf |
| 科学技术类型(必须转化为double类型) | %e |
| 限制输出字段宽度 | %x.yf (x:整数长度,y:小数点长度) |
待解问题，在linux kernel里面也有使用bool来定义变量，查看code，定义如下：
typedef _Bool bool;
但是并没有真正找到具体定义在何处，待解。
下面是stdbool.h的source code：
#define _STDBOOL_H #ifndef __cplusplus #define bool _Bool #define true 1 #define false 0 #else /* __cplusplus */ /* Supporting _Bool in C++ is a GCC extension. */ #define _Bool bool #if __cplusplus <201103l>
也大致解释了linux kernel bool type了。
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