Case Insensitive String comp in C

Question

I have two postcodes char* that I want to compare, ignoring case. Is there a function to do this?

Or do I have to loop through each use the tolower func

Answer 1

You can get an idea, how to implement an efficient one, if you don't have any in the library, from here

It use a table for all 256 chars.

• in that table for all chars, except letters - used its ascii codes.
• for upper case letter codes - the table list codes of lower cased symbols.

then we just need to traverse a strings and compare our table cells for a given chars:

const char *cm = charmap,
        *us1 = (const char *)s1,
        *us2 = (const char *)s2;
while (cm[*us1] == cm[*us2++])
    if (*us1++ == '\0')
        return (0);
return (cm[*us1] - cm[*--us2]);