C语言 C 编译器警告未知转义序列 '\.' c程序中使用正则表达式
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C compiler warning Unknown escape sequence '\.' using regex for c program
提问by c_sharp
I am using regex to determine a command line argument has the .dat extension. I am trying the following regex:
我正在使用正则表达式来确定命令行参数具有 .dat 扩展名。我正在尝试以下正则表达式：
#define to_find "^.*\.(dat)?"
For some reason I am getting the warning I stated in the title of this question. First, is this expression correct? I believe it is. Second, if it is correct, how can i get rid of this warning?
出于某种原因，我收到了我在这个问题的标题中提到的警告。首先，这个表达是否正确？我相信是的。其次，如果它是正确的，我怎样才能摆脱这个警告？
I am coding a c program in Xcode and the above #define is in my .h file. Thanks!
我正在 Xcode 中编写 ac 程序，上面的 #define 在我的 .h 文件中。谢谢！
回答by dasblinkenlight
The warning is coming from the C compiler. It is telling you that \.is not a known escape sequence in C. Since this string is going to a regex engine, you need to double-escape the slash, like this:
警告来自 C 编译器。它告诉您这\.不是 C 中已知的转义序列。由于此字符串将进入正则表达式引擎，因此您需要对斜杠进行双重转义，如下所示：
#define to_find "^.*\.(dat)?"
This regex would match a string with an optional .datextension, with datbeing optional. However, the dot .is required. If you want the dot to be optional as well, put it inside the parentheses, like this: ^.*(\\.dat)?.
此正则表达式将匹配具有可选.dat扩展名的字符串，并且dat是可选的。但是，点.是必需的。如果你想点是可选的还有，把它放在括号内，像这样：^.*(\\.dat)?。
Note that you can avoid escaping the individual metacharacters by enclosing them in square brackets, like this:
请注意，您可以通过将单个元字符括在方括号中来避免转义它们，如下所示：
#define to_find "^.*([.]dat)?"
回答by Ed Heal
You need
你需要
#define to_find "^.*\.(dat)?"
Should do the trick as the \ needs to be escaped for C and not the benefit for regex at this stage
应该做到这一点，因为 \ 需要为 C 转义，而不是现阶段正则表达式的好处
