c++ 解决无法打印uint8_t 类型变量的问题

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 <cstdint>
#include <iostream>
#include <typeinfo>
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
/* Defining these macros in C++98 is a GCC extension. */
#define bool bool
#define false false
#define true true
#endif
#endif /* __cplusplus */
/* Signal that all the definitions are present. */
#define __bool_true_false_are_defined 1
#endif /* stdbool.h */

也大致解释了linux kernel bool type了。

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