Hi, experts, I using boost.regex parse the content-type header's value in MIME. A typical content-type's BNF like following: Content-Type = "Content-Type:" SP media-type media-type = type "/" subtype *( ";" gen-param ) type = token subtype = token gen-param = pname [ "=" pval ] pname = token pval = token / quoted-string An example content-type as following: multipart/mixed; boundary="theboundary" ;id=33 There may be zero or one more parameters in content-type. My parse code as following: #include #include <iostream> #include <string> #define COUT(x) std::cout << x << std::endl #define VAR(v) std::cout << #v << ": " << v << std::endl #define TOKEN "[a-zA-Z0-9]+" #define TYPE "(" TOKEN ")" #define SUBTYPE "(" TOKEN ")" #define PNAME "(" TOKEN ")" #define PVALUE "(" TOKEN ")" #define PARAM "(;" PNAME "=" PVALUE ")" #define CONTENT_TYPE_EXPRESS TYPE "/" SUBTYPE PARAM "*" int main() { std::string ct("multipart/mixed;boundary=theboundary;id=33"); COUT(CONTENT_TYPE_EXPRESS); boost::regex regex_content_type(CONTENT_TYPE_EXPRESS); boost::smatch result; if (boost::regex_match(ct, result, regex_content_type)) { VAR(result.size()); for (unsigned int i=0; i