You can use a variable to read input which you want to ignore. If you are simply skipping single characters, something like this should work:
char ignoreChar;
is >> ignoreChar; // Should be a '['
// for loop goes here
is >> ignore; // Shoudl be a ']'
You might want to add if statements to make sure the ignored character is in fact what you expect it to be.
Alternatively, you can read in a whole line as a string and extract the information you want from there. This is called string parsing.