scs@adam.pika.mit.edu (Steve Summit) (04/08/89)
In article <1383@auspex.auspex.com> guy@auspex.auspex.com (Guy Harris) correctly points out that: >..."fflush" doesn't >flush input, so the ANSI standard says nothing new - it says "it flushes >output, we make no claims about input", which reflects current practice >(S5R3's "fflush" appears to flush input, although it's not documented - >which is kind of obnoxious; either it's a useful feature, in which case >it should be documented and supported, or it's a useless one, in which >case it shouldn't have been put in... (Rahul Dhesi made essentially the same point earlier.) The trouble with fflush on an input stream is that it isn't analogous to fflush on an output stream. fflush on an output stream means "do the write right now;" however, no equivalent interpretation is meaningful for an input stream. Packages that I know of that do allow fflush on an input stream instead discard the contents of the buffer, which is very different from what fflush on an output stream does. I'm contemplating adding fabort(FILE *) to my stdio library-- this would discard the buffer contents from an input or output stream, without doing any I/O. For an input stream, this would be equivalent to what those extended fflush'es apparently do, but it avoids the nonportable overloading, while admitting the possibility of an orthogonal operation on an output stream. Once upon a time I wanted such a thing for an output stream, perhaps for use in a control-C handler. (I can't remember now; fabort probably wouldn't have helped anyway.) Comments? Steve Summit scs@adam.pika.mit.edu
whitbeck@sanjuan.wrcr.unr.edu (Mike Whitbeck) (05/31/91)
I have a problem using fscanf() and fgets() and was wondering
if it had something to do with fflush() {I guess I just don't
know what fflush() is for!}
I open a file
fp = fopen("file","r");
and then I read some stuff
fscanf(fp,"%f\n",&fv);
then later I try to suck in a line as a text string
fgets(str,n,fp);
Elsewhere I have used fgets() to read in a line
but here it fails! (gets only the first 'word' (whitespace
delimited) from the line.
As a workaround I use a loop
for (...) {
fscanf(fp,"%s",dummy);
strcat(line," ");
strcat(line,dummy);
}
ICK!
What's going on here? Is fscanf() known to mess up fgets()? or
is this unique to me? [I am using a SUN 3/80].
HELP!torek@elf.ee.lbl.gov (Chris Torek) (05/31/91)
In article <456@equinox.unr.edu> whitbeck@sanjuan.UUCP (Mike Whitbeck) writes: >I have a problem using fscanf() and fgets() and was wondering >if it had something to do with fflush() {I guess I just don't >know what fflush() is for!} Fflush() is for output files only (despite anything POSIX says to the contrary; only output flush is reasonably portable). It means `take anything that I asked you to write earlier, and do your darnedest to see that it gets written'. Normally, a putchar, printf, fwrite, or other output operation really means `do this eventually'. Fflush means `It is now ``eventually''.' >I open a file > fp = fopen("file","r"); >and then I read some stuff > fscanf(fp,"%f\n",&fv); >then later I try to suck in a line as a text string > fgets(str,n,fp); >Elsewhere I have used fgets() to read in a line >but here it fails! (gets only the first 'word' (whitespace >delimited) from the line. This suggests, but does not prove, that there is a bug in the implementation you are using. To prove it you must produce a complete program (preferably as small as possible), not just code fragments. -- In-Real-Life: Chris Torek, Lawrence Berkeley Lab CSE/EE (+1 415 486 5427) Berkeley, CA Domain: torek@ee.lbl.gov
darwinl@alliance.uucp (Darwin Ling) (06/04/91)
In article <456@equinox.unr.edu> whitbeck@sanjuan.UUCP (Mike Whitbeck) writes: >I have a problem using fscanf() and fgets() and was wondering >if it had something to do with fflush() {I guess I just don't >know what fflush() is for!} > >I open a file > fp = fopen("file","r"); > >and then I read some stuff > fscanf(fp,"%f\n",&fv); >then later I try to suck in a line as a text string > fgets(str,n,fp); >Elsewhere I have used fgets() to read in a line >but here it fails! (gets only the first 'word' (whitespace >delimited) from the line. >As a workaround I use a loop > for (...) { > fscanf(fp,"%s",dummy); > strcat(line," "); > strcat(line,dummy); > } >ICK! > >What's going on here? Is fscanf() known to mess up fgets()? or >is this unique to me? [I am using a SUN 3/80]. > >HELP! One possible problem is that your buffer's size , namely str's size, may not be big enough to store all the characters that you read from the file... Make sure you have allocated enough memory for str... ------------------------------------------------------------------ Darwin Ling Alliance Technologies , Inc Advanced Development group uunet : uunet!alliance!darwinl ------------------------------------------------------------------