Thread: Theoretical question regarding text files

Hello,
I was just wondering whether or not it is possible to "mix" characters and integer values in a text document that is to be read by C.

I am to read and use values for length around the hip, neck and such, however, most of the tutoring examples I am finding online seem to strictly deal with either integers or characters alone.

Basicly my text file looks a bit like:
Abdominal length: 90.000
Neck length: 26.500
and so on

So, before I move further into this subject, is it possible at all to isolate and use only the double values or will I have to format my text file differently?

You can have whatever type of data you want in a file, and mix text, numbers, binary data, etc. As long as you know how it is stored, you can extract the parts you want. In your case, it wouldn't be too difficult. I would read in a line with fgets. Then, I would either use sscanf or a combination of, say strtok and strtod, to extract the double values.

Right, I get the logic behind that. I can make it read and scan the first line of my text document succesfully.
How would you make it switch to the next line and repeat the process? A loop with a condition like textfile != EOF or something like that?

Originally Posted by anduril462

EDIT: You should get in the habit of trying little experiments for stuff like this. The worst that happens is your program crashes, best case it works. You'll learn much more by trying/experimenting yourself than if you come here straight away for all your questions.

Yeah, thats what I've heard is the best way to learn, which I've also tried to practice.. I made other adjustments for my program this evening and just needed to lay it off for a bit, so I thought a healthy brainstorm and discussing here might do the trick before I go to bed. I'll pick it up in the morning.

Thank you!

What am I doing wrong here? It seems so simple, yet, it doesn't work.

Code:

    printf("%s", tekst); /* tekst is a string "Body fat percent is: 24.325" */ 
    sscanf(tekst, "%lf", BFpercent); /* Want to scan the string for an accurance of a double and store it in BFpercent */
    printf("%lf", BFpercent); /* BFpercent comes out as 0.000 */

Compile with warnings turned all the way up, you have an error somewhere. I can't tell without seeing the definition, but either your sscanf or the printf of BFpercent is wrong. printf takes a double to use with "%lf". I think it's the sscanf that's wrong, you need a & in front of the BFpercent so scanf gets the address of BFpercent, and knows where to store the value it scans.

Also, check the documentation for scanf (emphasis mine): sscanf(3): input format conversion - Linux man page

Originally Posted by man sscanf

RETURN VALUE These functions return the number of input items successfully matched and assigned, which
can be fewer than provided for, or even zero in the event of an early matching failure.

You should check the return value of sscanf and ensure it works before proceeding, and assuming BFpercent has a value:

Code:

if (sscanf(tekst, "%lf", &BFpercent) != 1) {
    // could not scat BFpercent, handle error -- perhaps print something and exit
}

Lastly, sscanf doesn't just skip ahead to any double. The first thing in the format string is a %lf, so sscanf expects the first thing in tekst to be a double. It's not, so the match fails. If you know the start to tekst will be fixed, put it in the sscanf literally:

Code:

if (sscanf(tekst, "Body fat percent is: %lf", &BFpercent) != 1)

Oooh yeah, bugger!

Forgot that tiny & in the scan. All the small things! It seems to work now, after implementing vart's code.