for (int i = 0; i < 10; i++);

…但不是这样：

for (int i = 0; i < 10; i++)

这看起来很琐碎，直到你意识到开始和结束括号之间的文本可能包含其他括号，例如：

for (int i = funcA(); i < funcB(); i++);

我使用python.re模块。现在我的正则表达式看起来像这样(我留下了我的意见，所以你可以更容易理解)：

# match any line that begins with a "for" or "while" statement:
^\s*(for|while)\s*
\(  # match the initial opening parenthesis
    # Now make a named group 'balanced' which matches a balanced substring.
    (?P<balanced>
        # A balanced substring is either something that is not a parenthesis:
        [^()]
        | # …or a parenthesised string:
        \( # A parenthesised string begins with an opening parenthesis
            (?P=balanced)* # …followed by a sequence of balanced substrings
        \) # …and ends with a closing parenthesis
    )*  # Look for a sequence of balanced substrings
\)  # Finally,the outer closing parenthesis.
# must end with a semi-colon to match:
\s*;\s*

这对于所有上述情况都是完美的，但是一旦你尝试并且使for循环的第三部分包含一个函数，它就会中断，像这样：

for (int i = 0; i < 10; doSomethingTo(i));

我认为它打破，因为只要你在开始和结束括号之间放置一些文本，“平衡”组匹配包含文本，因此(？P =平衡)部分不再工作，因为它不会匹配(由于括号内的文本不同的事实)。

在我的Python代码中，我使用VERBOSE和MULTILINE标志，并创建如下的正则表达式：

REGEX_STR = r"""# match any line that begins with a "for" or "while" statement:
^\s*(for|while)\s*
\(  # match the initial opening parenthesis
    # Now make a named group 'balanced' which matches
    # a balanced substring.
    (?P<balanced>
        # A balanced substring is either something that is not a parenthesis:
        [^()]
        | # …or a parenthesised string:
        \( # A parenthesised string begins with an opening parenthesis
            (?P=balanced)* # …followed by a sequence of balanced substrings
        \) # …and ends with a closing parenthesis
    )*  # Look for a sequence of balanced substrings
\)  # Finally,the outer closing parenthesis.
# must end with a semi-colon to match:
\s*;\s*"""

REGEX_OBJ = re.compile(REGEX_STR,re.MULTILINE| re.VERBOSE)

任何人都可以建议改进这个正则表达式？它变得太复杂，我不能让我的头。