Arduino convert constant char to unsigned long - variables

Question

I'm asking you to know how to convert a constant char variable[] to a unsigned long variable!
The problem doesn't exist if not for :
I've to convert this value for example "0x20DF10EF" if I convert it to long it return me back "551489775".
What i want is to receive back "0x20DF10EF"!
Hope i've explained well enough my problem!
Best regards D.Tibe!
---- Edit ----
while(O != 'I'){
if(reciver.decode(&results)){
CMD[i] = "0x" + String(results.value, HEX);
CMD[i].toUpperCase();
Val[0] = CMD[i].c_str();
//Vil[0] = CMD[i].c_str();
//for(int i = 0; i < sizeof(Val[0])-1 ;i++)
//{
//}
Byte = String(results.bits, DEC);
delay(1000);
O = 'I';
reciver.resume();
}
This is my code!
I have to convert my Val[0] (that is a Constant char) to Unsigned long variable.
Like said before i'll have a value like this 0x20DF10EF in my constant char and i want to get exactly the same on my unsigned long variable, SO :
Val[0] will be = to 0x20DF10EF and i want to get back the same value but into the unsigned long variable like this
unsigned long Var will be = to 0x20DF10EF

Answer 1

If I understood correctly, you want to parse a const char * string with an hex number and put it into a variable.
If this is correct, there are two ways: using the sscanf function or converting it by hand.
Method 1:
unsigned long result;
if (sscanf(Val[0], "0x%x", &result) != 1)
{
Serial.println("Val[0] is not a valid hex value");
}
Method 2:
unsigned long result = 0;
byte i;
for (i = 2; i < strlen(Val[0]); i++)
{
if ((Val[0][i] >= '0') && (Val[0][i] <= '9'))
{
result = (result << 4) + Val[0][i] - '0';
}
else if ((Val[0][i] >= 'A') && (Val[0][i] <= 'F'))
{
result = (result << 4) + 10 + Val[0][i] - 'A';
}
else if ((Val[0][i] >= 'a') && (Val[0][i] <= 'f'))
{
result = (result << 4) + 10 + Val[0][i] - 'a';
}
else
{
Serial.println("Val[0] is not a valid hex value");
break;
}
}
By the way, adding 0x in front of the string is useless for this conversion. If you can, remove it and then replace "0x%x" with "%x" in the sscanf solution, or i = 2 with i = 0 in the hand-made one.