On Thu, Oct 28, 2010 at 1:41 AM, Eric Niebler wrote:

You might find the interface less than ideal. C++ doesn't allow strings as template parameters.

-- Eric Niebler BoostPro Computing http://www.boostpro.com

Hi Eric, just a question: It is possible to pass array objects with external linkage as template parameters, is there any way one can manipulate them at compile time? I am wondering, if one can pass begin and end iterator as template parameters and verify such a string. That might have real impact on compile time... If I can use such a function: tempalte void array_len(char (&arr)[]) {} I might be able to pass instantiated function template function to the template to calculate the string length and than I have begin and length of the string, and can apply recusion at compile time. What do you think about it? With Kind Regards, Ovanes

Eric Niebler wrote:

On 10/27/2010 2:46 PM, Stiles Watson wrote:

...

I'm a new to metaprogramming so please bare with the stupid questions:

I have a requirement to convert string literals to a specified format at compile-time. In otherwords, given a literal like "3A689", I need to verify the value and, if not valid, generate a correct value such that:

//pseudocode const char ch[] = verify<"3A689">::valid_value;

would result in something like:

const char ch[] = "03A689X";

Can I use Boost to write a template to do this?

I know that is extremely vague, but does anyone have any thoughts?

Use mpl::string:

http://www.boost.org/doc/libs/1_44_0/libs/mpl/doc/refmanual/string.html

You might find the interface less than ideal. C++ doesn't allow strings as template parameters.

Thanks Eric. Question. For the example given at the link above, it has typedef mpl::string<'hell','o wo','rld'> hello; Why would it not be typedef mpl::string<'h','e','l','l','o',' ','w','o','r','l','d'> hello; OR if the example is correct, why could you not simply do typedef mpl::string<'hello world'> hello; Like I said, I'm new to this so I'm sure there is something fundamental that I'm missing. Stiles

Question. For the example given at the link above, it has

typedef mpl::string<'hell','o wo','rld'> hello;

That's weird.

Why would it not be

typedef mpl::string<'h','e','l','l','o', ' ','w','o','r','l','d'> hello;

I would think this was correct, as well.

OR if the example is correct, why could you not simply do

typedef mpl::string<'hello world'> hello;

Non-type template arguments can only be constant integers or (maybe in this case) multi-byte characters. A four-byte character value might be the standard limit here. (To be honest, I haven't really worked with Unicode or anything else beyond one-byte characters. Someone else may have a better answer for you.) Cromwell D. Enage