[Error] cannot convert 'std::string {aka std::basic_string<char>}' to 'const char*' for argument '1' to 'FILE* fopen(const char*, const char*)'

具体代码：

string defi="D:\\HappyGames\\CL\\1.0\\";
    string defis="\\passwords.tmp";
    defi=defi+s;
    defi=defi+defis;
    FILE*passin=fopen(defi,"r");