C语言 如何在 C 中正确地将十六进制字符串转换为字节数组？
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How to correctly convert a Hex String to Byte Array in C?
提问by Alex
I need to convert a string, containing hex values as characters, into a byte array. Although this has been answered already hereas the first answer, I get the following error:
我需要将包含十六进制值作为字符的字符串转换为字节数组。虽然这里已经作为第一个答案回答了这个问题，但我收到以下错误：
warning: ISO C90 does not support the ‘hh' gnu_scanf length modifier [-Wformat]
Since I do not like warnings, and the omission of hhjust creates another warning
因为我不喜欢警告，而省略hh只是造成另一个警告
warning: format ‘%x' expects argument of type ‘unsigned int *', but argument 3 has type ‘unsigned char *' [-Wformat]
my question is: How to do this right? For completion, I post the example code here again:
我的问题是：如何正确地做到这一点？为了完成，我再次在此处发布示例代码：
#include <stdio.h>
int main(int argc, char **argv)
{
const char hexstring[] = "deadbeef10203040b00b1e50", *pos = hexstring;
unsigned char val[12];
size_t count = 0;
/* WARNING: no sanitization or error-checking whatsoever */
for(count = 0; count < sizeof(val)/sizeof(val[0]); count++) {
sscanf(pos, "%2hhx", &val[count]);
pos += 2 * sizeof(char);
}
printf("0x");
for(count = 0; count < sizeof(val)/sizeof(val[0]); count++)
printf("%02x", val[count]);
printf("\n");
return(0);
}
采纳答案by mvp
You can use strtol()instead.
你可以strtol()改用。
Simply replace this line:
只需替换此行：
sscanf(pos, "%2hhx", &val[count]);
with:
和：
char buf[10];
sprintf(buf, "0x%c%c", pos[0], pos[1]);
val[count] = strtol(buf, NULL, 0);
UPDATE: You can avoid using sprintf()using this snippet instead:
更新：您可以避免sprintf()使用此代码段：
char buf[5] = {"0", "x", pos[0], pos[1], 0};
val[count] = strtol(buf, NULL, 0);
回答by caf
You can either switch your compiler to C99 mode (the hhlength modifier was standardised in C99), or you can use an unsigned inttemporary variable:
您可以将编译器切换到 C99 模式（hh长度修饰符在 C99 中标准化），也可以使用unsigned int临时变量：
unsigned int byteval;
if (sscanf(pos, "%2x", &byteval) != 1)
{
/* format error */
}
val[count] = byteval;
回答by Henri Socha
Why not do it without using sscanf, strol, etc. Below is HexToBin and as a free-bee, BinToHex. (Note originally there were returned enum error codes through an error logging system not a simple -1 return.)
为什么不使用 sscanf、strol 等来实现呢？下面是 HexToBin 和免费的 BinToHex。（注意最初通过错误记录系统返回了枚举错误代码，而不是简单的 -1 返回。）
unsigned char HexChar (char c)
{
if ('0' <= c && c <= '9') return (unsigned char)(c - '0');
if ('A' <= c && c <= 'F') return (unsigned char)(c - 'A' + 10);
if ('a' <= c && c <= 'f') return (unsigned char)(c - 'a' + 10);
return 0xFF;
}
int HexToBin (const char* s, unsigned char * buff, int length)
{
int result;
if (!s || !buff || length <= 0) return -1;
for (result = 0; *s; ++result)
{
unsigned char msn = HexChar(*s++);
if (msn == 0xFF) return -1;
unsigned char lsn = HexChar(*s++);
if (lsn == 0xFF) return -1;
unsigned char bin = (msn << 4) + lsn;
if (length-- <= 0) return -1;
*buff++ = bin;
}
return result;
}
void BinToHex (const unsigned char * buff, int length, char * output, int outLength)
{
char binHex[] = "0123456789ABCDEF";
if (!output || outLength < 4) return;
*output = '//convert hexstring to len bytes of data
//returns 0 on success, -1 on error
//data is a buffer of at least len bytes
//hexstring is upper or lower case hexadecimal, NOT prepended with "0x"
int hex2data(unsigned char *data, const unsigned char *hexstring, unsigned int len)
{
unsigned const char *pos = hexstring;
char *endptr;
size_t count = 0;
if ((hexstring[0] == '##代码##') || (strlen(hexstring) % 2)) {
//hexstring contains no data
//or hexstring has an odd length
return -1;
}
for(count = 0; count < len; count++) {
char buf[5] = {'0', 'x', pos[0], pos[1], 0};
data[count] = strtol(buf, &endptr, 0);
pos += 2 * sizeof(char);
if (endptr[0] != '##代码##') {
//non-hexadecimal character encountered
return -1;
}
}
return 0;
}
';
if (!buff || length <= 0 || outLength <= 2 * length)
{
memcpy(output, "ERR", 4);
return;
}
for (; length > 0; --length, outLength -= 2)
{
unsigned char byte = *buff++;
*output++ = binHex[(byte >> 4) & 0x0F];
*output++ = binHex[byte & 0x0F];
}
if (outLength-- <= 0) return;
*output++ = '##代码##';
}
回答by runeks
Using mvp's suggested change, I created this function which includes error checking (invalid characters and uneven length).
使用 mvp 的建议更改，我创建了此功能，其中包括错误检查（无效字符和长度不均匀）。
This function will convert a hexadecimal string - NOT prepended with "0x" - with an even number of characters to the number of bytes specified. It will return -1 if it encounters an invalid character, or if the hex string has an odd length, and 0 on success.
此函数会将十六进制字符串 - 不以“0x”开头 - 具有偶数个字符转换为指定的字节数。如果遇到无效字符，或者十六进制字符串的长度为奇数，它将返回 -1，成功则返回 0。
##代码##