点在正则表达式中（regex）

Question

I am using slre ( https://code.google.com/p/slre/ ) for providing a regex library for ac program.

I want to match an IP address with following pattern: "^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$"

I get following compile error: Warning: unknown excape sequence '\\.' I also tried it with '\\\\.' --> the compile error is gone, but it's still saying it doesn't match.

   if (!slre_compile(&slre, settings[i].regex)) {
       printf("Error compiling RE: %s\n", slre.err_str);
   } 
   else if (!slre_match(&slre, settings[i].value, strlen(settings[i].value), captures)) {
       printf("\nSetting '%s' does not match the regular expression!", settings[i].internName);
   }

settings[i].regex is a char* with the regular expression I mentioned above settings[i].value is a char* the string I am trying to match is 8.8.8.8

Is there any other way to check for a dot?

Answer 1

Try [.]

Dot isn't special inside character class.

Answer 2

The C compiler is seeing your backslash as an attempt to escape a character in C, in the same way that \\n becomes a newline. You need to use a double-backslash:

\\.

The C compiler will turn that into a single backslash and pass that to the regex library.

That's the source of the compiler warning - if it's still not matching after you add the extra backslash then you have a different problem as well.

According to http://derekslager.com/blog/posts/2007/09/a-better-dotnet-regular-expression-tester.ashx your regex does match 8.8.8.8 , so the problem isn't with the regex itself.

Answer 3

Your question is about C, but if you can compile with C++11 you can have a look to literal raw string

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2442.htm

std::string literal_string = R"literal string\. \n";