[ Article crossposted from comp.lang.c++ ]
[ Author was David Rogers ]
[ Posted on Sun, 9 Jul 1995 18:46:43 GMT ]

/* istrstream test program
 * Dave Rogers - drogers@cs.washington.edu
 * 7/9/95
 * This toy program demonstrates what I find to be an anomoly
 * with istreams: the extraction operator for an istream and a
 * char * does not stop for a null character in the stream.
 *
 * Borland's implementation blasts through the null character until
 * it hits the end of the buffer or a whitespace character. Is this
 * the norm?
 *
 * Can anyone explain why this behavior is desireable? This doesn't
 * happen with the other extraction operators.  For the record,
 * I think that a null should terminate extraction with the null,
 * just as an extraction of an int terminates with the first non-digit.
 * Subsequent extraction attempts would lead to fail begin set, just as
 * with an integer extraction encountering an initial non-digit.
 *
 * I was unable to find this issue adressed in the April 28th WP or in the
 * FAQ. I think it will arise frequently enough that a "standard behavior"
 * should be defined and documented.
 */

#include <strstream.h>

int main(int, char*[])
{
 // establish a line buffer
 const int BUF_SIZE = 128;
 char buffer[BUF_SIZE+1];

 // and a string buffer
 char string[BUF_SIZE+1];

 // and an istrstream for incore formatting
 istrstream source(buffer, BUF_SIZE);

 while (cin) {
  cin.getline(buffer, BUF_SIZE);
  // now that buffer is loaded, clear any old errors
  // and reseek to start of buffer
  source.clear(0);
  source.seekg(0, ios::beg);
  while (source) {
//   int string;   // uncomment to compare behavior
   if (source >> string) cout << string << endl;
  }
 }
 return 0;
}

drogers@grizzly.cs.washington.edu (David Rogers) writes:

> * This toy program demonstrates what I find to be an anomoly
> * with istreams: the extraction operator for an istream and a
> * char * does not stop for a null character in the stream.
> *
> * Borland's implementation blasts through the null character until
> * it hits the end of the buffer or a whitespace character. Is this
> * the norm?

Yes. The extractor for char* stops on whitespace, and a null
character is not whitespace. If you  want to stop on a null (or
a comma, or any other non-whitespace character), you will have to
use some other extraction method. You have several choices.

A null character terminates a literal character array, and is
used as a terminator for the C library string functions, but
has no special significance in a file.

--
Steve Clamage, stephen.clamage@eng.sun.com