Hi Bob



 BL>   How the bloody hell do I read part of a string in C?

 BL>

 BL>   I've got 3:711/934.12 and I want to read the 711. How do I do it?

 BL>

 BL>   In Pascal I'd use COPY("3:711/934.12",3,3); but how do
you pick a

 BL> string out of a string in C?



Most of the string handling functions in C start with str. Check

the library reference.



Use a pointer (to char) to point to the first char of the

substring you want to pull out, then use strncpy() to get it out.

Because strncpy() doesn't always guarantee to null terminate its

result, we do this ourselves afterwards.



        char dest[4];

        char *source = "3:711/934.12";

        char *p;



        p = source + 2;

        strncpy (dest, p, 3);

        dest[3] = "\0";



You could also write



        source += 2;       /* point "source" at the 3rd char */

        strncpy (dest, source, 3);

        dest[3] = "\0";



because source is just a pointer to char, but you can start to lose

track of where the original string started if you're not careful.



The function strtok() is probably better here. It walks its way

through a string, replacing the delimiter characters you supply in

the 2nd parameter with nulls, splitting the string up into

null-terminated stringlets (tokens). It will work on

"33:71/9034.45", where the above strncpy() demo won't. Note that it

modifies the source string.



This demo (copied pretty well straight from the library reference)

doesn't explicitly find the 2nd substring, it just prints the lot:



        p = strtok (source, "/:.");  /* find 1st stringlet */

        while (p)  /* strtok will return NULL when finished */

         {

          printf ("%s\n", p);

          p = strtok (NULL, "/:.");  /* find the next stringlet */

         }



That's the general case, which assumes that you don't know what

order the delimiters are going to appear, and that you don't know

how many tokens there will be. If you already know the form of the

string, use



        p = strtok (source, ":");  /* find 1st token */

        cout << p << endl;         /* print it */

        p = strtok (NULL, "/");    /* find next token */

        strcpy (dest, p); /*copy it out. p is already null-terminated*/

        cout << p << endl;         /* etc etc */

        p = strtok (NULL, ".");

        cout << p << endl;



(a bit of gratuitous C++ thrown in cos I like printf only a bit

more than scanf...)



Cheers





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