Topics 1.File Basics 2.Output Formatting 3.Passing File Stream Objects to Functions 4.More Detailed Error Testing 5.Member Functions for Reading and 6.Writing Binary Files

File Basics  A file—set of data stored permanently on an external storage device—e.g., hard disk, USB drive, etc.  Programs can read from and write to files.  File types  Binary files / Text files  Sequential / Random files  Program files / Data files  Image files / Audio files / Video files  Application files (Word, Excel) / Application Data files (.doc,.docx,.xls, xlsx) 13-3

Basic Steps in Using a File 1.Open the file 2.Use (read from, write to) the file 3.Close the file 13-4

File Stream Objects  Use of files requires file stream objects  There are three types of file stream objects (1) ifstream objects: used for input (2) ofstream objects: used for output (3) fstream objects: used for both input and output 13-5 Computer MemoryExternal Storage A B C D E A B C D E F G H I J K L M N O P Q R S T Ifstream infile myfile.dat

Opening a File for Input  Create an ifstream object in your program ifstream inFile;  Open the file by passing its name to the stream’s open member function inFile.open("myfile.dat"); 13-6

Getting File Name from User  Define file stream object, variable to hold file name ifstream inFile; char fileName[81]; // C-string  Prompt user to enter filename and read the filename cout << "Enter filename: "; cin.getline(fileName, 81);  Open the file inFile.open(fileName); 13-7

Using C++ string instead of C-string  Define file stream object, variable to hold file name ifstream inFile; string fileName;  Prompt user to enter filename and read the filename cout << "Enter filename: "; getline(cin, fileName);  Open the file inFile.open(fileName.c_str()); // Note: string to C-string conversion 13-8

Opening a File for Output  Create an ofstream object in your program ofstream outFile;  Open the file by passing its name to the stream’s open member function outFile.open("myfile.dat"); 13-9

Detecting File Open Errors Two methods for detecting if a file open failes (1) Call fail() on the stream inFile.open("myfile"); if (inFile.fail()) { cout << "Can't open file"; exit(1); } 13-10

Detecting File Open Errors (2) Test the status of the stream using the ! operator inFile.open("myfile"); if (!inFile) { cout << "Can't open file"; exit(1); } 13-11

Using fail() to detect eof Example of reading all integers in a file //attempt a read int x; infile >> x; while (!infile.fail()) { //success, so not eof cout << x; //read again infile >> x; } 13-12

Your Turn  Write a program which allows the user to input 3 lines of text. The program writes each line to a file. It then reads those text lines from the file and echo prints them to the screen.

Passing File Stream Objects to Functions  File stream objects keep track of current read or write position in the file  Always use pass by reference when passing file stream object to function 13-14

Passing File Stream Objects to Functions //print file contents to screen void printFile(ifstream &fin); int main(){ ifstream fin; fin.open(“myfile.dat”); printFile(fin);... } 13-15

Passing File Stream Objects to Functions // print file contents to screen void printFile(ifstream &fin){ int x; fin >> x; while(!in.fail()){ cout << x << " "; fin >> x; } } 13-16

Passing File Stream Objects //Write to file void writeTo(ofstream &fout, int list[], int count); int main(){ int list[] = {2, 4, 6, 8, 10}; int count = 5; ofstream fout; fout.open(“myfile.dat”); writeTo(fout, list, count);... } 13-17

Passing File Stream Objects // Write to file void writeTo(ofstream &fout, int list[], int count); for (int i = 0; i < count; i++){ fout << list[i] << ‘ ‘; } } 13-18

Your Turn  Convert the preceding “Your Turn” program so that writing data to a file and reading data from the file use two user-defined functions.

Binary File  Binary Files contain numeric data without conversion to ASCII characters.  Storing 1234: in Text File: 1 in Binary File: ‘1’ ‘2’‘3’‘4’