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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