Reading in data from a string in C (like scanf)

Question

I've read in and stored a data file that I am processing into an array of char arrays, one char array for each line in the file and I now want to process the individual lines. I'm not however sure how to do this.

I read each line in like so:

/* Read the whole file into an array */
char read_lines[FILE_LENGTH][FILE_WIDTH];
for(i=0;i<FILE_LENGTH;i++) {
    fscanf(data_file, "%[^\n]", read_lines[i]);
    fscanf(data_file, "%[\n]", dump);
}

I need to read the data in each line which is formatted as %d\t%d\t%d\t%d\t%d and I'm not really sure how to read a specific variable into a scanf function. I know that fscanf() reads from a file and scanf() reads from user input, is there a function that reads from a variable?

I come from a python background and in python, I would just use the following code:

read_lines = open('file.txt').readlines()
for line in lines:
    i = lines.index(line)
    first[i], second[i], third[i], forth[i], fifth[i] = line.split('\t')

I really cannot see how to do the equivalent in C. I've done a fair bit of research but I couldn't find anything useful. Any help would be appreciated!

Thanks!

Andrew White · Accepted Answer · 2011-02-02 18:04:40Z

2

Perhaps check out sscanf. It is just like it's cousin scanf and fscanf but takes a string instead. Here is a snip from the above link.

The sscanf function accepts a string from which to read input, then, in a manner similar to printf and related functions, it accepts a template string and a series of related arguments. It tries to match the template string to the string from which it is reading input, using conversion specifier like those of printf.

answered Feb 2, 2011 at 18:04

Andrew White

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1 Comment

Durand Over a year ago

Ahhhh! Thanks a lot, sscanf didn't seem to come up in my searches, this is exactly what I need.

Foo Bah · Accepted Answer · 2011-02-02 18:08:21Z

0

You can use the strtok function [read the manpage] to split a string

e.g. http://www.gnu.org/s/libc/manual/html_node/Finding-Tokens-in-a-String.html

answered Feb 2, 2011 at 18:08

Foo Bah

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3 Comments

Durand Over a year ago

Thanks, this is quite useful, I'll probably use this in the future but I think using sscanf() is probably a simpler option in C whereas I chose to use split() in python because it was the simpler choice there.

Foo Bah Over a year ago

@Durand you can do a similar thing in python -- also, the python code you gave doesnt automatically interpret the fields as integers

Durand Over a year ago

Yeah, you would need to use: first[i], second[i], third[i], forth[i], fifth[i] = [int(i) for in line.split('\t')]

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