CS150 Introduction to Computer Science 1 Summary Don’t forget! Assignment is due on Wednesday, October 29, 2003. 2/24/2019 CS150 Introduction to Computer Science 1

Ifstreams and Ofstreams So far, we have been reading user input from the keyboard. We have also been writing the output of our programs directly to the screen. What if we want to read in a large amount of data that is stored in a file. What if we want to write a large amount of data and store it in a file. 2/24/2019 CS150 Introduction to Computer Science 1

Steps for External files include<fstream> Declare file variables (pointers) that will correspond to the files you are using Input files type: ifstream Output files type: ofstream Open file Use file for input/output Close files 2/24/2019 CS150 Introduction to Computer Science 1

Declaring File pointers ifstream ifil; ofstream ofil; File variables or pointers are the ways that you refer to the files you are using. Can specify which input/output file to use. May input from more than one file May output to more than one file 2/24/2019 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Opening files <fileptr>.open(<filename>) Same syntax for both input and output files Filename may be string literal or char array variable Example: ifstream ifil; ifil.open(“input.dat”); 2/24/2019 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Checking for errors Should check for errors opening file if(ifil.fail()) { cout << “Error opening input file “; exit(1); } Note: you must open files first before using them! 2/24/2019 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Using file pointers Use input file pointer wherever you use cin Examples: ifil >> ch; Output output file ptr wherever you use cout ofil << ch; Make sure to use correct file pointer! 2/24/2019 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Closing files Must do at end when file is finished ifil.close(); ofil.close(); Same syntax for input and output files 2/24/2019 CS150 Introduction to Computer Science 1

CS150 Introduction to Computer Science 1 Example #include<fstream> #include<iostream> #define inFile "in.txt" int main( void ) { ifstream ifil; //input stream string name; ifil.open(inFile); if (ifil.fail()) cout << "*** Error opening file" << endl; exit (1); } while (!ifil.eof()) ifil >> name; cout << name << " "; ifil.close(); return 0; 2/24/2019 CS150 Introduction to Computer Science 1