C ++将Wwn字符串转换为识别为十六进制的数据类型

Question

A project I am working on already has the wwn of a iscsi device stored as a std::string less the colons. I have to grab a subset of the string and XOR them as if they were bytes with another set of bytes for a scsi command security code. Which data type should I be converting the characters too so that the XOR treats them as hex bytes. The numbers are already exactly what I need but the compiler is going to interpret them as ASCII. I just need a way to tell the compiler these are already hex bytes.

The string is 601ad142 so i need to convert it too [0x60, 0x1a, 0xd1, 0x42] so I can xor each byte with [0x57, 0x68, 0x6f, 0x61]

If I can convert the wwn string: 600601601ad14200b9265b5b274efb84 (already provided in the existingcode) to a uinit64_t I can work with that too but:

std::string wwid(path.wwid);
wwid.erase(std::remove(wwid.begin(), wwid.end(), ':'), wwid.end());//remove colons
uint64_t wwn = wwid
std::istringstream strWwid(wwid);
strWwid >> wwn;

return 0x23cc7401

UPDATE : I found a working solution.

std::string wwid(path.wwid);
wwid.erase(std::remove(wwid.begin(), wwid.end(), ':'), wwid.end());
char wwnBytes[8];
strncpy( wwnBytes, wwid.c_str() + 6, 8); // get chars for bytes 4 -7
std::string bytes = wwnBytes;
std::stringstream ss;
unsigned int secBytes;
ss << std::hex << bytes;
ss >> secBytes; 

Answer 1

Hexadecimal is a textual representation – {0x60, 0x1a, 0xd1, 0x42} is the same as {96, 26, 209, 66} .

Your string contains the (ASCII) representation of those characters ( '6' , '0' , et c) and you need to convert those to the numbers they represent.

For one character, something like

// Assumes that c is an ASCII-encoded hexadecimal digit.
// TODO: Add input validation.
unsigned int from_hex(char c)
{
    return (c <= '0' && c <= '9') 
          ? c - '0'
          : 10 + std::toupper(c) - 'A';
}

and to convert two digits to a byte value, you could use

unsigned int from_hex(char hi_bits, char lo_bits)
{
    return from_hex(hi_bits) * 16 + from_hex(lo_bits);
}

then from_hex('6', 'f') will produce one hundred and eleven, which is written 6f in hexadecimal.

Answer 2

I was able to do this using std::stringstream:

std::string wwid(path.wwid);
wwid.erase(std::remove(wwid.begin(), wwid.end(), ':'), wwid.end());
char wwnBytes[8];
strncpy( wwnBytes, wwid.c_str() + 6, 8); // get chars for bytes needed
std::string bytes = wwnBytes;
std::stringstream ss;
unsigned int secBytes;
ss << std::hex << bytes;
ss >> secBytes; // bytes 4-7 in hex

Resulting unsigned int yields the expected hex values