将字符串转化为16进制数:

/*
// C prototype : void StrToHex(BYTE *pbDest, BYTE *pbSrc, int nLen)
// parameter(s): [OUT] pbDest - 输出缓冲区
// [IN] pbSrc - 字符串
// [IN] nLen - 16进制数的字节数(字符串的长度/2)
// return value:
// remarks : 将字符串转化为16进制数
*/
void StrToHex(BYTE *pbDest, BYTE *pbSrc, int nLen)
{
    char h1,h2;
    BYTE s1,s2;
    int i;

    for (i=0; i<nLen; i++)
    {
        h1 = pbSrc[2*i];
        h2 = pbSrc[2*i+1];

        s1 = toupper(h1) - 0x30;
        if (s1 > 9)
        {
            s1 -= 7;
        }

        s2 = toupper(h2) - 0x30;
        if (s2 > 9)
        {
            s2 -= 7;
        }

        pbDest[i] = s1*16 + s2;
    }
}

将16进制数转化为字符串:

/*
// C prototype : void HexToStr(BYTE *pbDest, BYTE *pbSrc, int nLen)
// parameter(s): [OUT] pbDest - 存放目标字符串
// [IN] pbSrc - 输入16进制数的起始地址
// [IN] nLen - 16进制数的字节数
// return value:
// remarks : 将16进制数转化为字符串
*/
void HexToStr(BYTE *pbDest, BYTE *pbSrc, int nLen)
{
    char ddl,ddh;
    int i;

    for (i=0; i<nLen; i++)
    {
        ddh = 48 + pbSrc[i] / 16;
        ddl = 48 + pbSrc[i] % 16;
        if (ddh > 57)
        {
            ddh = ddh + 7;
        }
        if (ddl > 57)
        {
            ddl = ddl + 7;
        }
        pbDest[i*2] = ddh;
        pbDest[i*2+1] = ddl;
    }

    pbDest[nLen*2] = '\0';
}

来源:
大厨无盐煮
https://www.cnblogs.com/nio-nio/p/3309367.html