Question

I have a multiline TSV file with the following format:

Type\tBasic Name\tAttribute\tA Long Description\n

As you can see, the Basic Name and the Description can both contain some number of spaces. I am trying to read each line in and extract the elements. For now, I’ve narrowed it down to just extracting the basic name. My fscanf is as follows:

fscanf(file_in, "%*[^ ]s\t%128[^ ]s\t%*[^ ]s\t%[^ ]s\n", name_string, desc_string);

This doesn’t work as I have hoped, and I’m having trouble narrowing down the error. Does anyone know how I could read in the lines properly?

Answer 1

I mostly agree with Pablo (that the scanf family don’t make great parsers), but it’s worth understanding how to write a scanf pattern. The pattern you’re looking for is something like this:

fscanf(" %*[^\t] %128[^\t] %*[^\t] %128[^\n]", name_string, desc_string)

Notes:

1. %[xyz] is a directive. %[xyz]s is two directives, the second of which matches a literal s

2. As far a I know, there is no way to match a single literal tab character, since any whitespace in the pattern matches any amount of whitespace (including none) in the input. I used a space in my example, which will match a terminating tab, but it will also match any number of consecutive tabs so empty fields won’t be parsed correctly.

3. The 128-character limit does not include the terminating NUL character.

4. Also, if the scan stops because the chracter limit is exceeded, it won’t skip the rest of the field automatically, so you’ll end up out of synch with the input.

A better pattern would be:

fscanf(" %*[^\t] %128[^\t]%*[^\t] %*[^\t] %128[^\n]%*[^\n]", name_string, desc_string)

which explicitly skips the remaining characters in the field, if necessary. An even better solution would be to use the a modifier and get fscanf to malloc memory for you.