formating string to hex and validate - c++-cli

Question

I have an application that accepts hex values from a C++/CLI richtextbox.
The string comes from a user input.
Sample input and expected output.
01 02 03 04 05 06 07 08 09 0A //good input
0102030405060708090A //bad input but can automatically be converted to good by adding spaces.
XX ZZ DD AA OO PP II UU HH SS //bad input this is not hex
01 000 00 00 00 00 00 01 001 0 //bad input hex is only 2 chars
How to write function:
1. Detect if input is good or bad input.
2. If its a bad input check what kind of bad input: no spaces, not hex, must be 2 chars split.
3. If its no spaces bad input then just add the spaces automatically.
So far I made a space checker by searching for a space like:
for ( int i = 2; i < input.size(); i++ )
{
if(inputpkt[i] == ' ')
{
cout << "good input" << endl;
i = i+2;
}
else
{
cout << "bad input. I will format for you" << endl;
}
}
But it doesn't really work as expected because it returns this:
01 000 //bad input
01 000 00 00 00 00 00 01 001 00 //good input
update
1 Check if input is actually hex:
bool ishex(std::string const& s)
{
return s.find_first_not_of("0123456789abcdefABCDEF ", 0) == std::string::npos;
}

Answer 1

Are you operating in C++/CLI, or in plain C++? You've got it tagged C++/CLI, but you're using std::string, not .Net System::String.
I suggest this as a general plan: First, split your large string into smaller ones based on any whitespace. For each individual string, make sure it only contains [0-9a-fA-F], and is a multiple of two characters long.
The implementation could go something like this:
array<Byte>^ ConvertString(String^ input)
{
List<System::Byte>^ output = gcnew List<System::Byte>();
// Splitting on a null string array makes it split on all whitespace.
array<String^>^ words = input->Split(
(array<String^>)nullptr,
StringSplitOptions::RemoveEmptyEntries);
for each(String^ word in words)
{
if(word->Length % 2 == 1) throw gcnew Exception("Invalid input string");
for(int i = 0; i < word->Length; i += 2)
{
output->Add((Byte)(GetHexValue(word[i]) << 4 + GetHexValue(word[i+1])));
}
}
return output->ToArray();
}
int GetHexValue(Char c) // Note: Upper case 'C' makes it System::Char
{
// If not [0-9a-fA-F], throw gcnew Exception("Invalid input string");
// If is [0-9a-fA-F], return integer between 0 and 15.
}