在C中解析具有不同大小的行的文本文件

Question

I have a program that reads lines from a text file and puts it in a list. The words on each line are categorized as command (add or remove element), position, product and price. They are always in that order. Some lines do not have price or product, just the command and position. I parse the lines correctly for the first few lines, but if the text file comes short of a few words, for example, doesn't tell us the price or product just the command and postion, I get a segfault. Is there a way for me to check if a line from the text file is shorter so that I can only parse the elements that are there?

The text file looks something like this:

add 0 staples 2
add 1 paper 4
add 1 tape 3
add 3 paperclips 2
remove 2
remove 0

The function to parse is as follows.

while (fgets (buff, 140, test))
{
    token = strtok(buff, " ");
    instructions = malloc(sizeof(char)*strlen(token)+1);
    strcpy(instructions, token);

    token = strtok(NULL, " ");
    listPosition = atoi(token);

    token = strtok(NULL, " ");
    product = malloc(sizeof(char)*strlen(token)+1);
    strcpy(product,token);

    token = strtok(NULL, " ");
    price = atoi(token);

Answer 1

Use delimiter for each line. Read each line up to the delimiter then parse that. You can also use delimiter after each in the input. Such as command;product;price; # command;product;price; # .

Choose delimiter that wont show up in your normal input youre reading in.

Answer 2

1. Use fgets function gets the line
2. Write a parse function, that takes a line and give you back 4 tokens (command, position, product etc). You can use space as delimeter.
3. Then you know at hand whats present, whats not