NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/lang/c/11689

Text File | 1992-07-28 | 3.5 KB | 90 lines

Newsgroups: comp.lang.c
Path: sparky!uunet!cs.utexas.edu!asuvax!ennews!envmsa.eas.asu.edu!ptran
From: [e-mail] (Phi-Long Tran)
Subject: Re: Checking variables for characters & Copying portions of strings
Message-ID: <[e-mail]>
News-Software: VAX/VMS VNEWS 1.4-b1
Sender: [e-mail] (USENET News System)
Organization: Arizona State University, Tempe, AZ
Date: Wed, 29 Jul 1992 04:22:00 GMT
Lines: 78

In article <[e-mail]>,
[e-mail] (William Moxley) writes...

> I'm adding an editing feature to a little database I wrote.  I need to be
> able to see if a certain variable has anything but whitespace in it.  (So
> that you can just hit enter past some of the fields instead of having to
> retype everything) How can I do this?  I've tried strlen and sizeof, but
> they just tell me how big the string is defined for.

     If all you want to do is determine if a string contains "whitespace",
try the following function.  It returns the location of the first non-white
character in its argument.  It calls "isspace" to determine if a character
is "whitespace".  The return value may be useful for later processing.  The
check for NULL is for safety reasons, such as when the caller is passing
function first_nonwhite the return value of another function, passing on
the responsibility of checking for NULL to the caller.  Using the routine,
a string is non-white if the return value is not NULL and does not point to
the null terminator.

char * str_firstnonwhite( const char *string )
{
   if (string == NULL) return NULL;
   while ((*string != '\0') && isspace(*string)) string++;
   return string;
}

> Also, an unrelated question.  How can you copy a portion of a string into
> another?  What I want to do is to take a part out of the middle section
> of string 1, and put it in the middle section of string 2.  I've looked
> at strncpy, but I don't know if/how it's possible to make it start from
> the middle of a string.

     It sounds like you want to insert one string into another, such as
inserting the string "Riding " into "Little Red Hood" at offset 11 to
produce "Litte Red Riding Hood".  First, we need to "shift" the destination
over by +n bytes, where n is the length of the string to insert (if n is 0,
we just call strcpy).  When we shift the destination string, we copy from
the null terminator of the string to the first character.  This avoids
overlapping problems.  After shifting, we copy the string to insert "into"
the destination string.

char * str_insert( char * pdest, const char * pinsert )
{
   int insertlen;
   int idest;

   if (pdest == NULL) return NULL;
   if ((pinsert == NULL) || (*pinsert == '\0')) return pdest;

   if (*pdest == '\0') return strcpy(pdest, pinsert);

   insertlen = strlen(pinsert);
   for (idest = strlen(pdest); idest >= 0; idest --)
      pdest[idest + insertlen] = pdest[idest];
   return strncpy(pdest, pinsert, insertlen);
}

Example:

     char test_buffer[40];

     strcpy(test_buffer, "Little Red Hood");
     str_insert(&test_buffer[11], "Riding ");

     @ = null terminator.
                    1    1    2    2    3
              0....5....0....5....0....5....0
     Before:  test_buffer Little Red Hood@
     After:   test_buffer Little Red Riding Hood@

     This might not be exactly what you want, but maybe it'll give you some
ideas.  Notice that the routine assumes there is enough room to insert
pinsert.

---
Phi-Long Tran
[e-mail]
Arizona State University