regex_merge/string.c_str() - why temp var?

From: ke7_at_[hidden]
Date: 2001-10-14 16:51:52

// Hi.

#include "boost/regex.hpp"

// Why does

        std::string str1;

        const char *pcc1 = (str1 =
                boost::regex_merge((std::string)"foobar",
                (boost::regex)"o", "uu")).c_str();

// work, but

        const char *pcc2 = ( /* nothing */
                boost::regex_merge((std::string)"foobar",
                (boost::regex)"o","uu")).c_str();

// does not work? IOWs, why is the assignment to a temporary variable
necessary?