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Reading multiple columns in C++

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# 15  
Old 03-13-2013
It's probably better to use "strtod()" or "atof()" to convert a string to a double, if only because "sscanf()" can and does do weird things when input is not as expected. "strtod()" also provides the ability to know the last character processed, so it's easier to tell if something went bad.
This User Gave Thanks to achenle For This Post:
emily
# 16  
Old 03-13-2013
Can even be done in shell with bc for the floating point, something like:
Code:
while read a b c
do
 f=$(
  ( echo 'e=0
n=0'
    for d in $c
    do
     echo 'n=n+1
e=e+'"$d"
    done
    echo e/n
   ) | bc -l | sed 's/\.*0*$' )
 echo $a $b $f
done <in_file >out_file

I second the sscanf() concerns. I like to validate my inputs -- never give inputs the benefit of the doubt. The man says atof() is strtod() with less error checking. You get to choose. And that is UNIX in a nutshell: lots of options, support for quick, devil-may-care code, but the wise chose the more robust alternatives.
Last edited by DGPickett; 03-13-2013 at 04:24 PM..
# 17  
Old 03-13-2013
hi,
Thanks for the reply..but I am confuses, I need to plot both columns, how am I suppose to plot them the?
So you propose to use shell script to make them like single valued columns..and then call in C++ code to plot?

emily,
Quote:
Originally Posted by DGPickett
Can even be done in shell with bc for the floating point, something like:
Code:
while read a b c
do
 f=$(
  ( echo 'e=0
n=0'
    for d in $c
    do
     echo 'n=n+1
e=e+'"$d"
    done
    echo e/n
   ) | bc -l | sed 's/\.*0*$' )
 echo $a $b $f
done <in_file >out_file

# 18  
Old 03-13-2013
I am sure there are shell friendly graph programs, too. Heck, you can lay down images in text and then call utilities to make them into images! I am never shy about using a popen() to read shell output in C/C++! You can use system() to make an named pipe and sort it to itself, so all you have to do is write the named pipe and then read it. Unlike COBOL, no embedded sort! Smilie
Code:
system( "(mknod p p ; sort -o p p ; rm p )&" );
FILE *f = fopen( "p", "w" );
while (...) { ... fputs( buf, f ); ... }
fclose( f );
f = fopen( "p", "r" );
while ( fgets( buf, sizeof( buf ), f )){...}
fclose( f );
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