Obtains a reference to thestd::sub_match object representing the target sequence between the start of the beginning of the target sequence and the start of the entire match of the regular expression.

ready() must betrue. Otherwise, the behavior is undefined.

[edit]Return value

Reference to the unmatched prefix.

[edit]Example

#include <iostream>#include <regex>#include <string> int main(){std::regex re("a(a)*b");std::string target("baaaby");std::smatch sm; std::regex_search(target, sm, re);std::cout<< sm.prefix().str()<<'\n';}

b

[edit]See also

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