how do open a .txt using system();

#include<iostream>
#include<string>
#include<fstream>

using namespace std;

int main(){
string file;
cout <<"enter file name";
cin  >> file;
system(file);
}

is there an a way to open a txt file by using the user input. i only know for example system("code.txt"); but what if if it is user-defined. please help.