Parsing Variable # of Data Fields after fgets

[Michael R. Copeland]

I'm processing a control file comprised of many types of lines, with
some containing variable data. I have a problem parsing the following
data:
18 12.2 7.145 6.214 Phase distances
First, I've read the entire line and have manually extracted the
record type (18). Now I must parse the (3) real values that follow,
only knowing (from other data previously read) that there are 3 values
there. The number of blanks separating the fields can vary, too.
I can use sscanf, I suppose, by coding a series of switch-based calls
that have 1-n %f format specifiers and 1-n array element references -
but that's cumbersome and limiting (if I encounter more data than I've
coded for). There must be a way to do this common sort of thing, but I
can't see it. 8<{{ Any thoughts? TIA

 

[Richard Heathfield]

Michael R. Copeland said:

I'm processing a control file comprised of many types of lines, with
some containing variable data. I have a problem parsing the following
data:
18 12.2 7.145 6.214 Phase distances
First, I've read the entire line and have manually extracted the
record type (18). Now I must parse the (3) real values that follow,
only knowing (from other data previously read) that there are 3 values
there. The number of blanks separating the fields can vary, too.
I can use sscanf, I suppose, by coding a series of switch-based calls
that have 1-n %f format specifiers and 1-n array element references -
but that's cumbersome and limiting (if I encounter more data than I've
coded for). There must be a way to do this common sort of thing, but I
can't see it. 8<{{ Any thoughts? TIA

Consider the wonderful flexibility that a loop offers you.

 

[Michael R. Copeland]

I have a problem parsing the following data:

Consider the wonderful flexibility that a loop offers you.

Sure...but _how_ do I do it? With sscanf? Some other way? If
sscanf, please explain how it's done.

 

[Gordon Burditt]

I have a problem parsing the following data:

Sure...but _how_ do I do it? With sscanf? Some other way? If
sscanf, please explain how it's done.

Functions such as strtol(), strtod(), and strtoul() give you back
a pointer to the *END* of the data it used for the number. If it's
NULL, there was an error, if it's not, that's a good starting point
for looking for the next number.

Gordon L. Burditt

 

[Stan Milam]

Sure...but _how_ do I do it? With sscanf? Some other way? If
sscanf, please explain how it's done.

#include <stdio.h>

int
main( void )
{
int x;
double a, b, c;
char inbuf[100];
char string[] = "18 12.2 7.145 6.214 Phase Differences\n";

sscanf(string, "%d", &x);
switch( x ) {
case 18 :
sscanf( string,
"%*d %lf %lf %lf %[^\n]%*c",
&a,
&b,
&c,
inbuf
);
break;

default :
break;
}

printf("%lf %lf %lf %s\n", a, b, c, inbuf);
return 0;
}

 

[Stan Milam]

Sure...but _how_ do I do it? With sscanf? Some other way? If
sscanf, please explain how it's done.

I forgot to mention that sscanf() is great for this kind of application.
It is very powerful and you should grab your manual and read
thouroughly how it works. And, there are other ways to do it also. If
you want I'll post another example of a different way to do it.

Stan.

 

[Chuck F.]

>
Sure...but _how_ do I do it? With sscanf? Some other way? If
sscanf, please explain how it's done.

Please do not remove attribution lines for material you quote.

For example:

double realvals[3];
integer i, rectype;

if (1 != scanf("%d", &rectype) barf();
else {
switch (rectype) {
....
18: for (i = 0; i < 3; i++) {
if (1 != scanf{"%d", %realvals) {
barf(); break;
}
dothingswith(realvals);
flushln(stdin); /* NOT fflush, you write this */
break;
....
default:
barf(); /* unknown rectype */
}
}

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More details at: <http://cfaj.freeshell.org/google/>

 

[Richard Heathfield]

Michael R. Copeland said:

Sure...but _how_ do I do it? With sscanf? Some other way? If
sscanf, please explain how it's done.

find n, the number of fields on the line (which, apparently, you can do
already), and then do this:

for(i = 0; i < n; i++)
{
read a field from the line into array element, and don't lose track of
how far you've got along the line
}


Sure you could use sscanf. Or strtod. Or a home-rolled routine. Or whatever.
C is a very flexible language.

Personally, for this, I'd use a function that captures a whole line as a
string - I have a home-rolled routine for doing this but you could use
fgets if your inputs are sufficiently tame - and then do the conversions
using strtod, because it facilitates progressing neatly through the string.