How to use sscanf

Hi ,

I need to read in a txt file with below syntax:

  # This is text file:
  # color : number : exist : [OLD_STUFF]
  PRODUCT: abc
  orange    : 230 : 1,4,6,8,11,44-67,88    
  purple : 127 : 3,9,22,55-77,99 : OLD_STUFF

  PRODUCT: xyz
  white    : 230 : 1,4,6,8,11,88
  black : 130 : 3,9,22,99 : OLD_STUFF
  blue    : 679 : 0-11, 100-237, 239

1. how to write sscanf to read in a file that generic enough,
   if see "#"  , no process
   no "#", further process

2.   if further process.
     how to write generic sscanf to read data from "orange    : 230 : 1,4,6,8,11,44-67,88"   and "black : 130 : 3,9,22,99 : OLD_STUFF"
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avizitConnect With a Mentor Commented:

1)sscanf doesn't read directly from a file , so you have to use some other funtion e.g fgets to read in a line from the file to a buffer


#include <stdio.h>
char line[LINE_MAX];

while (fgets(line, LINE_MAX, fp) != NULL) {       //careful with these constant values LINE_MAX

now that would have put a line ( depending on constant and also the file content ) in the buffer
now you have use sscanf to read from the buffer

so within the while loop you can have a sscanf()

as in

sscanf(line, "%c%s",ch,str);

if ( ch == '#'){
}else {
btw are you sure  you have to use sscanf ? cos sscanf cannot read directlyfrom a file .. its reads only from a buffer .
I think reading the line first and then deciding how to process is probably cleaner - certainly more flexible, but if you really want to scanf...

The following code produces this output:

Color: orange, #230, 1,4,6,8,11,44-67,88
Color: purple, #127, 3,9,22,55-77,99, OLD_STUFF
Color: white, #230, 1,4,6,8,11,88
Color: black, #130, 3,9,22,99, OLD_STUFF
Color: blue, #679, 0-11,

    FILE *stream = fopen(filename, "r");
    char color[32], exist[32], stuff[32];
    long number;
    int numFields = 0;
    while ( (numFields = fscanf(stream, "%s : %d : %s :%s", color, &number, exist, stuff)) > 0)
        if ( numFields > 1 )
            std::cout << "Color: " << color << ", #" << number << ", " << exist;
            if ( numFields > 3 ) std::cout << ", " << stuff;
            std::cout << std::endl;
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You should note that the fscanf is fragile.  If the input lines are not all formatted alike, it won't work.
grg99Connect With a Mentor Commented:
I would start at the beginning of the string, look at each character.
If you see a digit, sscanf("%d" ) it, if not, do the right thing depending on whether it is a comma or a dash.  Keep advancing the string pointer til you get to the end of line.

waysideConnect With a Mentor Commented:
@drichards: your code doesn't correctly handle the blue line.

How about this:

    while ( (numFields = fscanf(stream, "%s : %d : %^[:] : %s", color, &number, exist, stuff)) > 0)

This should put everything between the second and third colons into the exist string.

In fact for maximum flexibility of input format, this should probably be done for all the strings:

    while ( (numFields = fscanf(stream, "%^[:] : %d : %^[:] : %^[\r\n]", color, &number, exist, stuff)) > 0)
drichardsConnect With a Mentor Commented:
Yep.  Like I said, the scanf approach is very fragile.  This is a very limited set of inputs to test.  I can easily imagine others with similar seemingly minute differences that will also cause problems.

Unless I had guarantees about the exact line formats, I'd go with a more systematic approach of reading in the whole line, inspecting the first character and calling a parsing routine on lines of interest.
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