Question

求解一个c语言问题， 把字符转换位相应的十六进制数, 并存入一个字节中

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char atohex(char s)
{
char n = s;

if( n >= 'a' && n <= 'z')
n = n + 'A' - 'a';

if(n > 0x39) //alpha
return (n - 0x37);
else //number
return (n - 0x30);
}

char chartohex(char *str)
{
char code[3], temp;
memset(code, 0, 3);
memcpy(code, str, 2);

temp = atohex(code[0]);
printf("the temp is %x\n", temp);
temp = (temp << 4) & 0xF0;
printf("the temp is %x\n", temp);
temp |= atohex(code[1]);
printf("the code is %s\n", code);

//printbinary(temp);
printf("the temp is %x, the sizeof(temp) is %d\n", temp, sizeof(temp));
return (char)temp;
}

int main()
{

char *pstr = "aB";
char c, z;

c = chartohex(pstr);
printf("The c hex is %x\n", c);
z = c;
printf("The c dec is %d\n", z);

}

我系统输出是：
the temp is a
the temp is ffffffa0 //按照设计，这应该是a0， 怎么多出6个f ？？？下面两个也是一样
the code is aB
the temp is ffffffab, the sizeof(temp) is 1
The c hex is ffffffab
The c dec is -85

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char atohex(char s)
{
char n = s;

if( n >= 'a' && n <= 'z')
n = n + 'A' - 'a';

if(n > 0x39) //alpha
return (n - 0x37);
else //number
return (n - 0x30);
}

unsigned char chartohex(unsigned char *str)
{
unsigned char code[3];
unsigned char temp;
memset(code, 0, 3);
memcpy(code, str, 2);

temp = atohex(code[0]);
printf("the temp is %x\n", temp);
temp = (temp << 4) & 0xF0;
printf("the temp is %x\n", temp);
temp |= atohex(code[1]);
printf("the code is %s\n", code);

//printbinary(temp);
printf("the temp is %x, the sizeof(temp) is %d\n", temp, sizeof(temp));
return temp;
}

int main()
{

unsigned char pstr[] = "aB";
unsigned char c, z;

c = chartohex(pstr);
printf("The c hex is %x\n", c);
z = c;
printf("The c dec is %d\n", z);

return 0;
}