Streams Formatted output cout right setw2 i setw8

Streams

Formatted output cout << right << setw(2) << i << setw(8) << raise. To. Power(2, i) << endl; // Insertion operator << This program lists powers of two. Enter exponent limit: 10 0 1 1 2 2 4 3 8 4 16 5 32 6 64 7 128 8 256 9 512 10 1024

Output manipulator The manipulators that take parameters, you need to include <iomanip> • setw(n) Set the width of the next field. Transient property (it affects only the next value). • setprecision(digits) Set the precision for the stream to digits. Persistent property (it remains in effect until it is explicitly changed. ) • setfill(ch) Set the fill character for the stream to ch. By default, space are added to. . Persistent property.

Output manipulator (Persistent property) • • • left right fixed (3. 14) scientific (3. 14 E+00) showpoint noshowpoint • • • showpos (+) noshowpos uppercase (E) nouppercase (e) boolalpha (true) noboolalpha

Formatted output #include <iostream> #include <iomanip> #include <cmath> using namespace std; const double PI = 3. 14159265358979323846; const double SPEED_OF_LIGHT = 2. 99792458 E+8; const double FINE_STRUCTURE = 7. 2573525 E-3;

void print. Precision. Table() { cout << " prec | pi | speed of light | fine-structure" << endl; cout << "------+-------------+--------" << endl; for (int prec = 0; prec <= 6; prec += 2) { cout << setw(4) << prec << " |"; cout << " " << setw(12) << setprecision(prec) << PI << " |"; cout << " " << setw(16) << setprecision(prec) << SPEED_OF_LIGHT << " |"; cout << " " << setw(14) << setprecision(prec) << FINE_STRUCTURE << endl; } }

int main() { cout << uppercase << right; cout << "Default format: " << endl; print. Precision. Table(); cout << endl << "Fixed format: " << fixed << endl; print. Precision. Table(); cout << endl << "Scientific format: " << scientific << endl; print. Precision. Table(); return 0; }

Default format: prec | pi | speed of light | fine-structure ------+--------------------+------------0 | 3| 3 E+08 | 0. 007 2 | 3. 1 | 3 E+08 | 0. 0073 4 | 3. 142 | 2. 998 E+08 | 0. 007257 6 | 3. 14159 | 2. 99792 E+08 | 0. 00725735

Fixed format: prec | pi | speed of light | fine-structure ------+----------------------+----------0| 3| 299792458 | 0 2| 3. 14 | 299792458. 00 | 0. 01 4| 3. 1416 | 299792458. 0000 | 0. 0073 6| 3. 141593 | 299792458. 000000 | 0. 007257

Scientific format: prec | pi | speed of light | fine-structure ------+-------------------+----------0| 3 E+00 | 3 E+08 | 7 E-03 2| 3. 14 E+00 | 3. 00 E+08 | 7. 26 E-03 4 | 3. 1416 E+00 | 2. 9979 E+08 | 7. 2574 E-03 6 | 3. 141593 E+00 | 2. 997925 E+08 | 7. 257352 E-03

Formatted input int limit; cout << "Enter exponent limit: "; cin >> limit; // extraction operator >> char ch; cout << "Enter a single character: "; cin >> noskipws >> ch; • skipws • noskipws Persistent property

• Stream is an abstract representation of an input or output device that is a source of, or destination for, data.

• Stream is an abstract representation of an input or output device that is a source of, or destination for, data.

Using file streams • Reading or Writing a file in C++ – Declare a stream variable to refer to the file ifstream infile; ofstream outfile; – Open the file infile. open(“student. txt”); infile. open(filename. c_str()); // if the name of file stored in a // string variable named filename – Transfer the data – Close the file Infile. close();

Single character I/O int ch; while ((ch = infile. get()) != EOF) { cout. put(ch); }

Single character I/O • • #include <iostream> #include <fstream> #include <string> using namespace std;

string prompt. User. For. File(ifstream & infile, string prompt = ""); int main() { ifstream infile; prompt. User. For. File(infile, "Input file: "); while (true) { int ch = infile. get(); if (ch == EOF) break; cout. put(ch); } infile. close(); return 0; }

string prompt. User. For. File(ifstream & infile, string prompt) { while (true) { cout << prompt; string filename; getline(cin, filename); infile. open(filename. c_str()); if (!infile. fail()) return filename; infile. clear(); cout << "Unable to open file. Try again. " << endl; if (prompt == "") prompt = "Input file: "; } }

Single character I/O • How to read an integer represented as a string of decimal digits? • The library implementation cannot know that the number is finished until it reads character that is not a digit. • That character may be part of subsequent input. infile. unget();

Line oriented I/O while (true) { string line; getline(infile, line); if (infile. fail()) break; cout << line << endl; }

Formatted I/O int main() { ifstream infile; prompt. User. For. File(infile, "Input file: "); int total = 0; while (true) { int value; infile >> value; if (infile. fail()) break; // 1. reaching EOF 2. wrong char total += value; } infile. close(); cout << "The sum is " << total << endl; return 0; } // The program give no indication that an error has occurred.

Formatted I/O if (!infile. eof()) { error("Data error in file"); }

int main() { ifstream infile; prompt. User. For. File(infile, "Input file: "); int total = 0; while (true) { string line; getline(infile, line); if (infile. fail()) break; total += string. To. Integer(line); } infile. close(); cout << "The sum is " << total << endl; return 0; }

String streams int string. To. Integer(string str) { istringstream(str); int value; stream >> value >> ws; if (stream. fail() || !stream. eof()) { error("string. To. Integer: Illegal integer format"); } return value; }

String streams string integer. To. String(int n) { ostringstream; stream << n; return stream. str(); }

Console input int limit; cout << "Enter exponent limit: "; cin >> limit; What happens if the user tries to enter the value 16 but types the letter t instead of the digit 6?

int get. Integer(string prompt) { int value; string line; while (true) { cout << prompt; getline(cin, line); istringstream(line); stream >> value >> ws; if (!stream. fail() && stream. eof()) break; cout << "Illegal integer format. Try again. " << endl; } return value; }