c++:重载函数“regex_search”的实例与参数列表不匹配

For my c++ class, we have been given a "simple regular expression assignment". But every time I try to use regex_search() in Visual Studio Community 2015, I get "no instance of overloaded function "regex_search" matches the argument list". I mouse-over the error, and it tells me it wants (for one example) string, smatch, string; which is exactly what I give it. For my c++ class, we have been given a "simple