1. Chapter 10C++ for Java Programmers1 Chapter 10 Input/Output

2. Chapter 10C++ for Java Programmers2 Introduction Two competing I/O systems in C++. Standard I/O Library, stdio Stream I/O Library, iostream Never use both Libraries in the same program.

3. Chapter 10C++ for Java Programmers3 The stdio Library “Inherited” from the C language. Widely known and available. Based on stable and well-exercised libraries. Not as extendable or adaptable as the newer Stream I/O Library. For developing new programs, the Stream I/O Library is preferred.

4. Chapter 10C++ for Java Programmers4 Examples of stdio # include // or stdio.h int c = getchar(); // read a single input character putchar('x'); // print a single character char * text = "please enter your name:"; puts(text); // print the text string char buffer[120]; gets(buffer); // read a line of input FILE * fp = fopen("mydata.dat", "r"); if (fp == NULL) puts("file cannot be opened"); fputc('z', fp); // write character to fp int c = fgetc(fp); // read character from fp char * msg = "unrecoverable program error"; fputs(msg, stderr); // write message to standard error output

5. Chapter 10C++ for Java Programmers5 Formatted Output The printf facility works only for formatted primitive values, such as integers and floats. Always verify that formatting commands match the argument types; compiler does not check

6. Chapter 10C++ for Java Programmers6 Examples of Formatted Output %dinteger decimal value %ointeger printed as octal %xinteger printed as hexadecimal %cinteger printed as character %uunsigned integer decimal value %ffloating point value %gfloating point value %snull terminated string value %percent sign

7. Chapter 10C++ for Java Programmers7 Exmples of printf int i = 3; int j = 7; double d = i / (double) j; printf("the value of %d over %d is %g", i, j, d); char * fileName =...; if (fopen(fileName, "r") == null) fprintf(stderr,"Cannot open file %s\n", fileName); char buffer[180]; sprintf(buffer, "the value is %d\n", sum); double d = 23.5; printf("the value is %d\n", d); // error -- float printed as int scanf("%d %f", &i, &f); // read an int, then a float

8. Chapter 10C++ for Java Programmers8 Problems with printf Works fine for built-in types, but Not easily expanded for new user- defined types Compiler cannot check formatting/argument agreement So, is there another way??

9. Chapter 10C++ for Java Programmers9 The Stream I/O Facility Whenever possible use the Stream I/O Library rather than the Standard I/O Library. Uses the ability to overload function names in C++. Better possibilities for extendability as well as improved error detection.

10. Chapter 10C++ for Java Programmers10 Stream output overloads << op ostream & operator << (ostream & out, const int value) { // print signed integer values on a stream unsigned int usvalue; if (value < 0)// print leading minus sign { out << '-'; usvalue = -value; } else // print non-negative number usvalue = value; out << usvalue; return out; }

11. Chapter 10C++ for Java Programmers11 Printing int as recursive fun inline char digitCharacter(unsigned int value) { return value + '0'; } ostream & operator << (ostream & out, const unsigned int value) { // print unsigned integer values on a stream if (value < 10) out << digitCharacter(value); else { out << (value / 10);// recursive call out << digitCharacter(value % 10); } return out; }

12. Chapter 10C++ for Java Programmers12 Complex output built in parts # include cout << "n " << n << " m " << m << " average " << (n+m)/2.0 << '\n';

13. Chapter 10C++ for Java Programmers13 Easy to extend to new types ostream & operator << (ostream & out, const rational & value) { // print representation of rational number on an output stream out << value.numerator() << '/' << value.denominator(); return out; } rational frac(3,4); cout << "fraction of " << 3 << " and " << 4 << " is “ << frac << endl;

14. Chapter 10C++ for Java Programmers14 I/O Manipulators A manipulator is used to change features of the I/O system. ostream & endl (ostream & out) { out << '\n'; // write the end of line character out.fflush(); // then flush the buffer return out; // then return the buffer } ostream & operator << (ostream & out, ostream & (*fun)(ostream &)) { return fun (out); // simply execute function }

15. Chapter 10C++ for Java Programmers15 Stream Input Stream input ignores white space. cin >> intval; while (cin >> intval) { // process intval... } // reach this point on end of input... Visualize >> and << as arrows Input operator, >> x : points data into x Output operator, << x : copies data out of x

16. Chapter 10C++ for Java Programmers16 File Streams A file stream is a stream that reads from or writes to a file. Must include the header file # include fstream header file includes the iostream header, so not necessary to include both. The class ifstream and ofstream are used to create streams that are attached to input and output files.

17. Chapter 10C++ for Java Programmers17 Conversion Operators A conversion operator changes a file stream into a boolean value, whereby the value indicates the success or failure of the file opening operation. char fileName = "outfile.dat"; ofstream ofd(fileName); // create file for output if (! ofd) { cerr << " cannot open file " << fileName } else { ofd << "first line in file"... } File operations in C++ throw far fewer exceptions than do in Java.

18. Chapter 10C++ for Java Programmers18 Test your Understanding What is the include file for the standard I/O library? How do you use the function printf? What are some problems with the printf function?

19. Chapter 10C++ for Java Programmers19 Test your Understanding What is the error? double pi = 3.14159; printf(“Pi is %d\n”, pi);

20. Chapter 10C++ for Java Programmers20 Test your Understanding What is the include file for the stream I/O facility? What operator is used for stream output? Why is this approach more easily extensible than the printf approach?