File input and output problems

fcuptfwfn

The following program can only write the content of s1 to a file, but cannot read it from the file. What is wrong?
#include<iostream>
#include<conio.h>
#include<fstream>


using namespace std;

int main()
{ofstream out("a.txt");
ifstream in("a.txt");
string s1,s2;

  s1="abcd 1234\n";
  out<<s1;
  in>>s2;

  cout<<"s2="<<s2<<endl;//s2 is empty~~~~

out.close();
in.close();
getch();
return 0;
}

水月痕

a.txt file needs path

yctoya

#include<iostream>
#include<conio.h>
#include<fstream>


using namespace std;

int main()
{ofstream out("a.txt");
ifstream in("a.txt");
string s1,s2;

  s1="abcd 1234\n";
  out<<s1;
out.close();
in>>s2;

  cout<<"s2="<<s2<<endl;//s2 is empty~~~~


in.close();
getch();
return 0;
}

fcuptfwfn

No need, a.txt is in the local project folder

xiaoshangls

The path is not a problem, but my vc6.0 cannot be compiled

xiaoshangls

Is there any lib to add?

fcuptfwfn

I want to create a file stream that can both input and output, so that I don’t need to create ifstream and ofstream. I don’t know what to do? The a.txt file is not created when the following program is running, so I don't know what is wrong.
#include<iostream>
#include<conio.h>
#include<fstream>


using namespace std;

int main()
{fstream file("a.txt",ios::in|ios::out);
string s1,s2;

  s1="abcd 1234\n";
  file<<s1; //Cannot write into a.txt
  file>>s2;
  cout<<"s2="<<s2<<endl;//s2 is empty
  
  file.close();

getch();
return 0;
}

julines

Problems with output buffering
#include<iostream>
#include<conio.h>
#include<fstream>
#include<string>

using namespace std;

int main()
{ofstream out("a.txt");
ifstream in("a.txt");
string s1,s2;

  s1="abcd 1234\n";
  out<<s1;
  out.close();//or out.flush();
  getline(in,s2);

  cout<<"s2="<<s2<<endl;//s2 is empty~~~~

in.close();
getch();
return 0;
}

julines

Before the file is closed and the buffer is not full, the string is not actually written to the file unless you manually refresh the stream.

yctoya

out<<s1;
  out.seekp(0);
// or out.close();
  in>>s2;