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Understanding File Input/Output in CS150: Essential Steps and Code Examples

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This guide provides an overview of file input and output operations in the CS150 Introduction to Computer Science course. It covers essential steps such as including the `` library, declaring file pointers for input and output, and methods for opening, using, and closing files. Practical examples are included to illustrate checking for errors when opening files and utilizing input/output file pointers. Ensure you understand these concepts for handling large data files effectively, as mastering them is crucial for your assignments and future programming projects.

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Understanding File Input/Output in CS150: Essential Steps and Code Examples

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

  2. 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. CS150 Introduction to Computer Science 1

  3. 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 CS150 Introduction to Computer Science 1

  4. 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 CS150 Introduction to Computer Science 1

  5. 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”); CS150 Introduction to Computer Science 1

  6. 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! CS150 Introduction to Computer Science 1

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

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

  9. 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; } CS150 Introduction to Computer Science 1

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