Convert hex string to binary array

strings.h

#pragma once

#include <windows.h>
#include <string>

// Helper functuion used by hex2bin() function.
inline int hex2byte(char c)
{
	if ((c >= '0') && (c <= '9'))
	{
		return c - '0';
	}
	if ((c >= 'A') && (c <= 'F'))
	{
		return c - 'A' + 10;
	}
	if ((c >= 'a') && (c <= 'f'))
	{
		return c - 'a' + 10;
	}
	return -1;
}

// Converts a hex string to a binary array.
// Returns NULL if string is not a hex array.
// NOTE: it's caller responsibility to free returned array with "delete[]".
inline unsigned char* hex2bin(const char* hex, size_t hexSize = -1)
{
	if (NULL == hex)
	{
		return NULL;
	}

	if (hexSize < 0)
	{
		hexSize = strlen(hex);
	}

	if ((hexSize % 2) != 0)
	{
		return NULL;
	}

	size_t binSize = hexSize / 2;
	unsigned char* bin = new unsigned char[binSize];

	size_t k = 0;
	for (size_t i = 0; i < binSize; i++)
	{
		int n1 = hex2byte(hex[k]);
		k++;
		int n2 = hex2byte(hex[k]);
		k++;

		if ((n1 < 0) || (n2 < 0))
		{
			delete[] bin;
			return NULL;
		}

		bin[i] = (n1 << 4) | n2;
	}

	return bin;
}