Buffering

• If I am planning to write data to a file, it’s better to collect the data and “write it” to the file all at once instead of writing data to the file line by line on the go.
• Collecting the data is called “buffering” the data.
• Writing to the file is called “flashing”, and we try to do that at the end.

#include <fstream>;
using namespace std;

int main(){
	ofstream outFile("myFile.txt");
	outFile << "ECE" << endl;
	outFile << "244" << endl;
	outFile.close();
	return 0;
}

The above example will flush to the file after “ECE” and also “244”. If we want to flash at the end, we can do two things: we can do the endl; or we can do flush().

#include <fstream>;
using namespace std;

int main(){
	ofstream outFile("myFile.txt");
	outFile << "ECE";
	outFile << "244";
	
	outFile << endl;
}

#include <fstream>;
using namespace std;

int main(){
	ofstream outFile("myFile.txt");
	outFile << "ECE";
	outFile << "244";
	
	outFile.flush();
}

Handling I/O Errors

• By default, the input streams are stored in a buffer (everything you write is buffered until you hit the enter key; after you press enter, it is sent to the program)
• whitespace, tab (4/8 whitespaces), newline are skipped

int x, y;
cin >> x >> y;

• Say you entered 101\\n75\\n
  • the first two whitespaces are ignored
  • the 101 is read until it sees the \\n, so the 101 is saved into x
  • the 75 is read until it sees the \\n, so the 75 is saved into y
• delimiters are `` \\t and \\n

What happens during error

int x, y;
cin >> x >> y;

• Say you entered 13. 37
  • the first number 13 is scanned with no issue in to x
  • cin cannot skip a ., but it’s still trying to save an integer into y, so we have an error

Summary:

• cin will read 13 into x, but it will not read . into y as it is not an integer.
• cin will fail silently.
• y is not affected (its value wasn’t scanned and changed), and the buffer is not affected.
• A flag is raised, and this flag will say cin is failing. This will affect all cin in the program unless we solve the issue.
  • cin.fail() = 1 if error
  • cin.fail() = 0 if no error

Solving Procedure