用C进行读，逐行操作和写出的最佳方法是什么？

Question

Suppose I have two text files in.txt and out.txt .

in.txt :

abc      one    2    3    4
         two    3    4    two    twenty
         three  3    20   8
adbc     two    4    28   3      thirty

How can I read line-by-line and operate when necessary? So that on any line I can check if it has some text in the first column ("abc" and "adbc" in this example), what's in the second column, third column, etc. until that line ends? Then, based on those operations write into out.txt ?

For example, if any line has its 6th column (if it has a 6th column) and it says "twenty" then print to out.txt "Hello."

or

If the second column is "three" add the following three numbers...

Answer 1

I don't know about BEST way but here's one way:

Read the file in and use strtok to parse it split up by delimiters. (Then you can use strtok again to read it split up by whitespace)

http://www.cplusplus.com/reference/cstring/strtok/

Answer 2

I think strtok can still get the job done. Just follow two different paths based on lines beginning with spaces.

pseudo code:

while (line = readline()) {
    if (line[0] == ' ') { // you can check for multiple spaces if necessary.
        // If line begins with empty first column
        tokenize_handle_normal(line);
    } else {
        // If line begins with string in the first column
        tokenize_handle_special(line); // Call tokenize_handle_normal(line) after parsing the first column
    }
}