How Can We Improve Regular Expressions to Reliably Detect C For and While Loops Ending with Semicolons?

Improving Regular Expression for C Loop Detection with Semicolon

Introduction

The original question sought a regular expression to identify C for or while loops terminated with a semicolon. A proposed solution utilized named capturing groups, but encountered challenges when function calls were included within the loop's third expression.

Enhanced Regular Expression

To resolve this issue, an alternative approach has been developed:

# match any line that begins with a "for" or "while" statement:
REGEX_STR = r"^\s*(for|while)\s*\("

# match a balanced substring, accounting for function calls within expressions:
SUB_STR_PATTERN = r"([^\(\)]|(\([^\(\)]*(?:\|\|[^()\s]*(?1))*?\)))"

# match a balanced string of arbitrary length, including function calls:
SUB_STR_GROUP = f"(?P<balanced>{SUB_STR_PATTERN})+"

# match the initial opening parenthesis, followed by balanced expressions, and finally the closing parenthesis.
REGEX_STR += f"{SUB_STR_GROUP}\)\s*;\s*"

# compile the regex object with MULTILINE and VERBOSE flags for readability
REGEX_OBJ = re.compile(REGEX_STR, re.MULTILINE | re.VERBOSE)

Explanation

This enhanced regular expression leverages the SUB_STR_PATTERN to define a balanced substring that can contain function calls. The || operator is used to create a logical OR condition, allowing the pattern to match either non-parenthetical characters or nested balanced strings.

By repeating this pattern within the SUB_STR_GROUP, the regex ensures that it can match a sequence of balanced expressions, regardless of their nesting level.

Conclusion

This improved regular expression provides a more robust solution for detecting C for or while loops terminated with a semicolon, even in cases where function calls are present within the loop's third expression. It simplifies the logic by eliminating the need for recursive patterns.

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