File I/O in C ++ II

1. File I/O in C++ II

2. Open() function The name of file • Open() is a member function in each classes ( fstream, ifstream, ofstream) • Voidfstream:: open ( const char *filename, openmodemode); • Voidifstream::open ( const char *filename, openmodemode= ios:: in); • Voidofstream:: open ( const char *filename, openmodemode= • ios:: out |iso :: trunc); Optiional to determine how the file is opened You can combine 2 or more of these value by ORing them together

3. File Open Mode

4. File Open Mode #include <fstream> using namespace std; void main() { ofstreamoutFile("file1.txt", ios::out); outFile << "That's new!\n"; outFile.close(); } If you want to set more than one open mode, just use the OR operator- |. This way: ios::ate | ios::binary

5. File format • In c++ files we (read from/ write to) them as a stream of characters • What if I want to write or read numbers ?

6. Example writing to file #include <iostream> #include <fstream> using namespace std; void main() { ofstreamoutFile; // open an exist file fout.txt outFile.open("number.txt",ios::app); if (!outFile.is_open()) { cout << " problem with opening the file ";} else {outFile<<200 <<endl ; cout << "done writing" <<endl;} outFile.close(); }

8. Example Reading from file #include <iostream> #include <fstream> #include <string> #include <sstream> using namespace std; void main() {//Declare and open a text file ifstreamINFile("number.txt"); string line; inttotal=0; while(! INFile.eof()) {//fetch line from number.txt and put it in a string getline(INFile, line); //converting line string to int stringstream(line) >> total; cout << line <<endl; cout <<total +1<<endl;} INFile.close(); // close the file }