[C++知识库]C语言第19天，数据的存储（一）

原码，反码，补码

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

int main() {
	int a = 20;//4个字节-32bit
	//00000000000000000000000000010100 - 原码
	//00000000000000000000000000010100 - 反码
	//00000000000000000000000000010100 - 补码
	//0x00000014
	int b = -10;
	//10000000000000000000000000001010 - 原码
	//11111111111111111111111111110101 - 补码
	//11111111111111111111111111110110 - 补码
	//0xfffffff6
	
	//对于整型来说：数据存放内存中其实存放的是补码

	1 - 1;
	//1+(-1)
	//00000000000000000000000000000001 -  1的补码
	//11111111111111111111111111111111 -  -1的补码
	//00000000000000000000000000000000 -  1+（-1）的补码 = 0的补码
	return 0;
}

求当前机器的字节序

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

//写一段代码求当前机器的字节序

check_sys() {
	int a = 1;
	char* p = (char*)&a;
	return *p;
}

int main() {
	//返回1，小端
	//返回0，大端
	int ret = check_sys();
	if (ret == 1) {
		printf("小端\n");
	}
	else {
		printf("大端\n");
	}
	
	return 0;
}

无符号

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

int main() {
	char a = -1;
	//1000000000000000000000000001 - -1的原码
	//1111111111111111111111111110 - -1的反码
	//1111111111111111111111111111 - -1的补码
	//11111111
	signed char b = -1;
	//11111111
	unsigned char c = -1;
	//11111111
	//0000000000000000000011111111
	printf("a=%d,b=%d,c=%d",a,b,c);//a=-1,b=-1,c=255

	printf("\n----------------------------\n");

	char d = -128;
	//100000000000000000000010000000-原码
	//111111111111111111111101111111-反码
	//111111111111111111111110000000-补码
	printf("%u\n", a);//4294967295
	//%d - 打印十进制的有符号数字
	//%u - 打印十进制的无符号数字
	return 0;
}

a=-1,b=-1,c=255
----------------------------
4294967295