How Can I Reliably Detect C 'for' and 'while' Loops Ending with a Semicolon?

Detecting C "for" and "while" Loops with Semi-Colon Termination

Matching C for or while loops that end with a semi-colon using a regular expression can be challenging. A common approach involves creating a named group to match balanced substrings, ensuring that the entire loop body is contained within parentheses.

However, this method falters when the loop body includes a function call, breaking the balance. A simplified approach using a non-regex function can overcome this issue.

Custom Function for Loop Matching

The following custom function takes an input string and searches for a for or while loop followed by a semi-colon:

def find_loop_and_semicolon(string):
    pos = string.find('(') + 1
    open_br = 0
    while open_br >= 0:
        char = string[pos]
        if char == '(':
            open_br += 1
        elif char == ')':
            open_br -= 1
        pos += 1
    return pos if open_br == 0 and string[pos] == ';' else -1

The function:

1. Sets the position counter pos to the position just before the opening bracket of the loop.
2. Initializes an open bracket counter open_br to 0.
3. Iterates through the string, incrementing open_br for opening brackets and decrementing it for closing brackets.
4. When open_br returns to 0, the position of the closing bracket is reached.
5. Checks if the character at the next position is a semi-colon to confirm loop termination.
6. Returns pos if both conditions are met or -1 otherwise.

Usage

string = "for (int i = 0; i < 10; doSomethingTo(i));"
result = find_loop_and_semicolon(string)
if result != -1:
    print("Loop found and terminated with a semi-colon.")
else:
    print("No matching loop found.")

Advantages

• Simplicity: The function is easy to understand and implement.
• Flexibility: It handles loops with complex bodies, including function calls.
• No Regex Overhead: Avoids the potential overhead and complexity of regular expressions.

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