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File I/O Examples
1. Write to a file
% cat fileEx1.cpp
// file i/o example - write to a file
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
// create an output file
ofstream file_out;
file_out.open( "testfile");
if( file_out.fail() ) // check for successful open
{
cout << "File was not successfully opened " <<
endl;
exit(1);
}
int num1 = 777, num2 = 888;
file_out << num1 << " " << num2 << " ";
return 0;
}
% g++ fileEx1.cpp
% a.out
% cat testfile
777 888
2. Read from a file
% cat fileEx2.cpp
// file i/o example - read from a file
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
// open an input file
ifstream file_in;
file_in.open( "testfile" );
if( file_in.fail() ) // check for successful open
{
cout << "File was not successfully opened " <<
endl;
exit(1);
}
int i1, i2;
file_in >> i1 >> i2;
cout << "Data read: " << i1 << " " <<
i2 << endl;
return 0;
}
% g++ fileEx2.cpp
% a.out
Data read: 777 888
3. Append to a file
% cat fileEx1.cpp
// file i/o example - add to a file
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
// create an output file
ofstream file_out;
file_out.open( "testfile", ios::app); // append
if( file_out.fail() ) // check for successful open
{
cout << "File was not successfully opened " <<
endl;
exit(1);
}
int num1 = 123, num2 = 456;
file_out << num1 << " " << num2 << " ";
return 0;
}
% g++ fileEx1.cpp
% a.out
% cat testfile
777 888 123 456
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