Question

I have a file like this:

10 15
something

I want to read this into tree variables, let’s say number1, number2, and mystring. I have doubts about what kind of pattern to give to fscanf. I am thinking something like this;

fscanf(fp,"%i %i\n%s",number1,number2,mystring);

Should this work, and also, is this the correct way of reading this file? If not, what would you suggest?

Answer 1

Read each line with fgets (or getline if you have it), split up the line with strsep (better, if available) or strtok_r (more awkward API but more portable), and then use strtoul to convert strings to numbers as necessary.

*scanf should never be used, because:

1. Some format strings (e.g. a bare "%s") are just as eager to overflow your buffers as gets is.
2. Behavior on integer overflow is undefined — invalid input can potentially crash your program.
3. They do not report the character position of the first scan error, making it nigh-impossible to recover from a parse error. (This can be somewhat mitigated by using fgets and then sscanf instead of fscanf.)