Hex to Bytes

Guest User

Hi

Please see my comments next to each coded expression and correct where necessary.

// Declare a static method which returns an array of bytes and accepts 1 input argument named hex of type string.
private static byte[] HexToBytes(string hex)

// Construct a new instance\object of type byte and pass the hex value and length property divided by two. Store the result in a local variable named bytes.
byte[] bytes = new byte[hex.Length / 2];

// Initialize i to 0, assign the hex Length property to be less than i / 2 and then iterate the loop with i++
for (int i = 0; i < hex.Length / 2; i++)

// Use the Substring method of string passing in the values i times 2 and 2 and then store the return value in a local variable named code.
string code = hex.Substring(i * 2, 2);

// Pass the code reference and the enum NumberStyles.HexNumber to the byte Parse method and then Set this to the reference bytes in position 0.
bytes[i] = byte.Parse(code, NumberStyles.HexNumber);

// Return the bytes reference.
return bytes;

Thanks

14 Replies

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Vulpes14y ago
Accepted answer
I've tried to look behind what the lines are actually doing rather than describing them literally in the following descriptions:

// Declare a static method which returns an array of bytes and accepts 1 input argument named hex of type string.
private static byte[] HexToBytes(string hex)

// Construct a new byte array whose length is half that of the hex string and store in a local variable named bytes.
byte[] bytes = new byte[hex.Length / 2];

// Initialize i to 0 and keep on adding 1 for each iteration as long as i is less than half of hex's length
for (int i = 0; i < hex.Length / 2; i++)

// Use the Substring method of the string class to extract the two characters of the hex string starting at index i * 2 and assign them to a local variable named code.

string code = hex.Substring(i * 2, 2);

// Convert the hexadecimal characters in code to a byte and assign this to the 'i'th element of bytes.
bytes[i] = byte.Parse(code, NumberStyles.HexNumber);

// Return the bytes array.
return bytes;
Vulpes14y ago
The reason why I didn't use a byte array in my example was because I wasn't interested in storing the results, just printing each one to the console so you could more easily see how the Substring() method was working.
Guest User14y ago
Thanks Vulpes

Just out of curiousity your example slightly differs from my example and I just wondered how it still works. For example I have provided both examples:-

My example

byte[] bytes = new byte[hex.Length / 2];

for (int i = 0; i < hex.Length / 2; i++)

string code = hex.Substring(i * 2, 2);

bytes[i] = byte.Parse(code, NumberStyles.HexNumber);

return bytes;

Your example

string hex = "A0B97762";

for (int i = 0; i < hex.Length/2; i++)

string byteStr = hex.Substring(i * 2, 2);

byte b = byte.Parse(byteStr, NumberStyles.HexNumber);

Console.WriteLine("i = {0}, 2 * i = {1}, byteStr = {2}, byte = {3}", i, i * 2, byteStr, b);

Obviously at first glance, in your example the local variable hex has been declared along with the Console.Writeline which makes sense. However in mine there is a new byte array declared ie byte[] bytes = new byte[hex.Length / 2]; and also the byte.Parse method is Set to the bytes array at first position ie bytes[i] = byte.Parse(code, NumberStyles.HexNumber);

Could you explain why this has been left out of your example please?

Thanks!
Vulpes14y ago
i * 2 is an expression which determines the starting index for the substring.

The next argument (2) tells the method how many characters to take from and including that index.

So, if you have this:

string hex = "A0B97762";
for (int i = 0; i < hex.Length/2; i++)
{
string byteStr = hex.Substring(i * 2, 2);
byte b = byte.Parse(byteStr, System.Globalization.NumberStyles.HexNumber);
Console.WriteLine("i = {0}, 2 * i = {1}, byteStr = {2}, byte = {3}", i, i * 2, byteStr, b);
}

the output will be this:

i = 0, 2 * i = 0, byteStr = A0, byte = 160
i = 1, 2 * i = 2, byteStr = B9, byte = 185
i = 2, 2 * i = 4, byteStr = 77, byte = 119
i = 3, 2 * i = 6, byteStr = 62, byte = 98
Guest User14y ago
Thanks Vulpes

Sorry to prolong this thread.

With the second argument of the Substring method being 2, how comes the method cannot work out that there will be 2 char pairs from the i * 2 statement? I dont see why 2 is needed, sorry for being dense here.

Thanks

Steven
Vulpes14y ago
Well, it's increasing by 2 each time.

So the successive values of i * 2 would be 0, 2, 4 and 6.

There are 8 characters in the string with indices from 0 to 7, so this would pick out successive character pairs.

The first argument to the Substring method is the starting index (i * 2 here) and the second argument is the number of characters to take (2 here).
Guest User14y ago
Vulpes

Another question if I may please...

Why would i * 2 iterate from 0 to 6 this would only make 7 chars not 8?

Also would it be the i * 2 that does the increments in 2 or the 2 length ie the 2nd passed in value?

Thanks
Guest User14y ago
Perfect I fully understand, thanks kindly Vulpes!
Vulpes14y ago
It's just in the interests of being able to do it generally within a loop.

If say the length of the string were 8, then as 'i' iterates from 0 to 3 in increments of 1 , then i * 2 will iterate from 0 to 6 in increments of 2 which is what we want here.
Guest User14y ago
Ok brilliant I understand.

So what would be the point of putting any multiplication ie i * 2 if it will always be zero?
Vulpes14y ago
Yes, i * 2 means take the value of i and multiply it by 2.

So, if i is zero, then i * 2 is also zero because the result of multiplying any number by zero is always zero.
Guest User14y ago
Thanks Vulpes

In your answer...

So, if i = 0, i * 2 is also 0 - how is this the case, surely i should still be 0 not i * 2 which would read i times 2?
Vulpes14y ago
In general, the expression s.Subtring(a, b) gets the 'b' characters of s, starting at index 'a' where the first character has an index of 0.

So, if i = 0, i * 2 is also 0 and hex.Subtring(i * 2, 2) therefore gets the first two characters of the hex string.

Similarly, if i = 1, the expression gets the next two characters of the string and so on.

So, if you have something like this:

hex = "4142";

the first two characters "41" will convert from hex to a byte with a decimal value of 65 which corresponds to the ASCII character 'A' and the second two characters "42" will convert to a byte with a value of 66 which corresponds to the ASCII character 'B'.
Guest User14y ago
Thanks Vulpes

Could I get clarification on the following expression please

string code = hex.Substring(i * 2, 2);

Given Substring(i * 2, 2) am I correct in saying that i * 2 will get the 2nd char in the string and then get a length of 2?

Thanks