Today’s Lecture I/O Streams Tools for File I/O Console I/O File I/O Tools for File I/O Sequential Access & Random Access to Files

Introduction Streams In C++ Special objects Deliver program input and output In C++ Console I/O is working with streams File I/O is also working with streams

Streams Stream: A flow of data Input stream Output stream Flow into program Can come from keyboard Can come from file Output stream Flow out of program Can go to screen Can go to file

Streams Usage We’ve used streams already cin cout Input stream object connected to keyboard cout Output stream object connected to screen

Stream Example int num1, num2, total; cout << "First number: "; cin >> num1; cout << "Second number: "; cin >> num2; total = num1 + num2; cout << “total = " << total << endl;

Streams Usage We’ve used streams already Can define other streams cin Input stream object connected to keyboard cout Output stream object connected to screen Can define other streams To or from files Used similarly as cin, cout

Streams Usage Examples: cin, cout Consider: Using the pre-defined stream cin int Number; cin >> Number; Reads value from stream (keyboard), assigned to Number Using the pre-defined stream cout cout << Number; Writes value to stream (monitor)

Streams Usage Like cin, cout Consider: Given program defines stream inStream that comes from some file: int Number; inStream >> Number; Reads value from stream (file), assigned to theNumber Program defines stream outStream that goes to some file outStream << theNumber; Writes value to stream, which goes to file

Files Reading from file Writing to file When program takes input Writing to file When program sends output Start at beginning of file (Sequential access) Other methods available

File Connection Must first create a file stream object Then connect the file to the file stream object For input only: File  ifstream object For output only: File  ofstream object Classes ifstream and ofstream Defined in library <fstream> Named in std namespace

File I/O Libraries To allow both file input and output in your program: #include <fstream> using namespace std;

Declaring Streams Objects (Variables) Stream must be declared like any other class variable: ifstream input_file_stream; ofstream out_file_stream; Must then "connect" to file: input_file_stream.open("infile.txt"); Called "opening the file" Uses member function open Can specify complete pathname

Streams Usage Once declared and connected, use it like cin and cout! int N; input_file_stream >> N; Output stream similar: ofstream output_file_stream; output_file_stream.open("outfile.txt"); output_file_stream << "Number = " << N;

Closing Files Files should be closed When program completed getting input or sending output Disconnects stream from file In action: input_file_stream.close(); output_file_stream.close();

File Example: Display 12.1 Simple File Input/Output (1 of 2)

File Example: Display 12.1 Simple File Input/Output (1 of 2)

Appending to a File Standard of stream open operation begins with empty file Even if file exists  contents lost Open for append: ofstream outStream; outStream.open("important.txt", ios::app); If file doesn’t exist  creates it If file exists  appends to end

Compare Console I/O and File I/O All cin functions are same for files! Read in (send out) integers (int) Read in (send out) characters (char) Read in (send out) floating-point s (float) …. For String operating: >> read one word (separated by spaces, new lines) getline() read one line of words

Compare Console I/O and File I/O (continued) For console String (C-string) operations char S[100]; cin >> S; read one word cin.getline(S, 20) ; read one line of words

Compare Console I/O and File I/O (continued) For file String (C-string) operations ifstream ifm; ifm.open("infile.txt"); char S[100]; ifm >> S; read one word ifm.getline(S, 20) ; read one line of words

Compare Console I/O and File I/O (continued) cout is same for file operations (say fout) ofstream fout; fout.open(“output.txt", ios::app); cout << “whatever\n” fout << “whatever\n” Whatever displayed on screen will be same as those saved in file

More I/O member functions See Appendix 4 of the textbook Stream_var.open(“File name”); Stream_var.close(); Strean_var.eof(); Stream_var.get(char_var); Stream_var.getline(cstring_var, length);

Checking End of File Use loop to process file until end An extraction operator actually returns a boolean value inStrem >> next Return true if the read was successful (space and new line will not be read) and returns false when code attempts to read beyond the end of the file Int next, sum =0; while (inStream >> next) { sum = sum + next; } cout << “ the sum is “ << sum << endl;

Checking End of File Use loop to process file until end inStrem.get(next) Return true if the read was successful and returns false when code attempts to read beyond the end of the file char next, sum =0; while (inStream.get(next)) { sum = sum + 1; } cout << “ the total number of characters is “ << sum << endl;

Checking End of File Use loop to process file until end inStrem.getline(next, length) Return true if the read was successful and returns false when code attempts to read beyond the end of the file Char[] next, sum =0; while (inStream.getline(next, 100)) { sum = sum + 1; } cout << “ the total number of lines is “ << sum << endl;

Which Function to Write The easiest one and works for any text data <<

Which Function to Read Numbers (Integer / floating-point) file: numbers are separated by blank space(s) >> Text file: words are separated by blank space(s): each word is going to be processed separately

Which Function to Read (continued) Character files each character (including space) needs to be processed individually get(char s) Ignore spaces, new lines, and tab >> Character files: one line is a record getline(char s[], int size)

Tools: File Names as Input Stream open operation Argument to open() is string type Can be literal (used so far) or variable char fileName[16]; ifstream inStream; cout << "Enter file name: "; cin >> fileName; inStream.open(fileName); Provides more flexibility

File Access Applications Copy files Copy char by char Copy line by line Process files: Determine how many specific characters Count words Count lines Work on numbers

Read and Write can be Performed at the Same Time Opens same as istream or ostream Adds second argument fstream rwStream; rwStream.open("stuff", ios::in | ios:: out); Opens with read and write capability It is confusing where to read and where to write: not recommend to use.

Random Access to Files Sequential Access Random Access Most commonly used So far we have talked about Random Access Rapid access to records Access "randomly" to any part of file

Random Access Tools Move about in file rwStream.seekp(1000); Positions put-pointer at 1000th byte rwStream.seekg(1000); Positions get-pointer at 1000th byte Not a requirement for this course

Summary of File Operations Read from a file Write to a new or existing file Delete a file Copy a file Move a file Modify a file