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-   -   can fscanf skip reading data conditionally? (http://www.velocityreviews.com/forums/t444557-can-fscanf-skip-reading-data-conditionally.html)

John 09-27-2006 03:54 PM

can fscanf skip reading data conditionally?
 
I need to read data from the file like the following with name and
score, but some line may only has name without score:

joe 100
amy 80
may

Here's my code, but it couldn't read the line with "may" because there
is no score. Anyone knows what is the workaround to this problem?

char name[20];
int score;

while (fscanf(ifp, "%s %d", name, &score) == 2)
{
printf("%s %d\n", name, score);
}


please advice. thanks!!


Fred Kleinschmidt 09-27-2006 04:37 PM

Re: can fscanf skip reading data conditionally?
 

"John" <javacc1@gmail.com> wrote in message
news:1159372487.763569.18800@i3g2000cwc.googlegrou ps.com...
>I need to read data from the file like the following with name and
> score, but some line may only has name without score:
>
> joe 100
> amy 80
> may
>
> Here's my code, but it couldn't read the line with "may" because there
> is no score. Anyone knows what is the workaround to this problem?
>
> char name[20];
> int score;
>
> while (fscanf(ifp, "%s %d", name, &score) == 2)
> {
> printf("%s %d\n", name, score);
> }
>


What makes you think it couldn't read the line?
I'll bet it did it just fine, and returned 1.

>
> please advice. thanks!!
>

--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Technical Architect, Software Reuse Project



Robert Gamble 09-27-2006 04:41 PM

Re: can fscanf skip reading data conditionally?
 
John wrote:
> I need to read data from the file like the following with name and
> score, but some line may only has name without score:
>
> joe 100
> amy 80
> may
>
> Here's my code, but it couldn't read the line with "may" because there
> is no score. Anyone knows what is the workaround to this problem?
>
> char name[20];
> int score;
>
> while (fscanf(ifp, "%s %d", name, &score) == 2)
> {
> printf("%s %d\n", name, score);
> }


int i;
while ((i = fscanf(ifp, "%s %d", name, &score)) >= 1)
{
if (i == 2)
printf("%s %d\n", name, score);
else
printf("%s\n", name);
}

Robert Gamble


Michael Mair 09-27-2006 04:46 PM

Re: can fscanf skip reading data conditionally?
 
John wrote:
> I need to read data from the file like the following with name and
> score, but some line may only has name without score:
>
> joe 100
> amy 80
> may
>
> Here's my code, but it couldn't read the line with "may" because there
> is no score. Anyone knows what is the workaround to this problem?
>
> char name[20];
> int score;
>
> while (fscanf(ifp, "%s %d", name, &score) == 2)
> {
> printf("%s %d\n", name, score);
> }


You did not specify what you want to do if you encounter this problem.
One example:

char name[20];
int score;
int ret;

while (EOF != (ret = fscanf(ifp, "%19s %d", name, &score)))
{
if (ret > 0) {
printf("%s", name);
if (ret > 1) {
printf("%d", score);
}
}
putchar('\n');
}

Next time, explain what you want to do, what you have, how the
results of your code do not match what you expected, and give
a compilable minimal example. This helps us help you.


Cheers
Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.

Keith Thompson 09-27-2006 08:07 PM

Re: can fscanf skip reading data conditionally?
 
"Robert Gamble" <rgamble99@gmail.com> writes:
> John wrote:
>> I need to read data from the file like the following with name and
>> score, but some line may only has name without score:
>>
>> joe 100
>> amy 80
>> may
>>
>> Here's my code, but it couldn't read the line with "may" because there
>> is no score. Anyone knows what is the workaround to this problem?
>>
>> char name[20];
>> int score;
>>
>> while (fscanf(ifp, "%s %d", name, &score) == 2)
>> {
>> printf("%s %d\n", name, score);
>> }

>
> int i;
> while ((i = fscanf(ifp, "%s %d", name, &score)) >= 1)
> {
> if (i == 2)
> printf("%s %d\n", name, score);
> else
> printf("%s\n", name);
> }


fscanf() skips whitespace, including newlines. If you call fscanf
with a format of "%s %d", it will read a blank delimited word, then
look for a decimal integer; if there isn't one on the current line, it
will continue reading lines until it finds either a decimal integer or
something that definitely isn't one.

That might happen to work, but it's fragile. Also, it won't detect
an error such as:

joe 100
amy 80
may

42

fred 97

(I'm assuming you want each name and optional score to be on a single
line.)

A better solution is to read an entire line at a time (use fgets() if
you can assume a maximum line length) and then apply sscanf() to the
resulting string.

An advantage of sscanf() is that it doesn't consume its input; you can
pass the same string to it again with a different format. Another
advantage is that, if the string contains a single line of input, it
won't try to read additional lines; it treats the end of the string
like end-of-file.

--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.


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