This question is the real question asked on StackOverflow. I'm here to review my answer and see how can I optimize it.

Here is the answer text:

This is a basic approach, but it proposes a proof of concept of what might be done. I do it using Bash along with the usage of the GCC -fsyntax-only option.

Here is the bash script:

#!/bin/bash
while IFS='' read -r line || [[ -n "$line" ]]; do
    LINE=`echo $line | grep -oP "(?<=//).*"`
    if [[ -n "$LINE" ]]; then
            echo $LINE | gcc -fsyntax-only -xc -
            if [[ $? -eq 0 ]]; then
                   sed -i "/$LINE/d" ./$1
            fi
    fi
done < "$1"

The approach I followed here was reading each line from the code file. Then, greping the text after the // delimiter (if exists) with the regex (?<=//).* and passing that to the gcc -fsyntax-only command to check whether it's a correct C/C++ statement or not. Notice that I've used the argument -xc - to pass the input to GCC from stdin (see my answer here to understand more). An important note, the c in -xc - specifies the language, which is C in this case, if you want it to be C++ you shall change it to -xc++.

Then, if GCC was able to successfully parse the statement (i.e., it's a legitimate C/C++ statement), I directly remove it using sed -i from the file passed.

Running it on your example (but after removing <- commented code from the third line to make it a legitimate statement):

// Those parameters control foo and bar... <- valid comment
int t = 5;
// int t = 10;
int k = 2*t;

Output (in the same file):

// Those parameters control foo and bar... <- valid comment
int t = 5;
int k = 2*t;

(if you want to add your modifications in a different file, just remove the -i from sed -i)

The script can be called just like: ./script.sh file.cpp, it may show several GCC errors while these are the correct