#include <fstream>#include <iostream>#include <string> int main(){std::string filename{"test.bin"};    std::fstream s{filename, s.binary| s.trunc| s.in| s.out}; if(!s.is_open())std::cout<<"failed to open "<< filename<<'\n';else{// writedouble d{3.14};        s.write(reinterpret_cast<char*>(&d), sizeof d);// binary output        s<<123<<"abc";// text output // for fstream, this moves the file position pointer (both put and get)        s.seekp(0); // read        d=2.71828;        s.read(reinterpret_cast<char*>(&d), sizeof d);// binary inputint n;std::string str;if(s>> n>> str)// text inputstd::cout<<"read back from file: "<< d<<' '<< n<<' '<< str<<'\n';}}

read back from file: 3.14 123 abc