Overview

FILE STREAM I/O

Data file streams can be used as an alternative to the standard i/o. To use the file commands, the ofstream/ifstream or fstream headers must be included:

ofstream.h output file

ifstream.h input file

fstream.h input & output file.

ofstream MyFile;

MyFile is a variable of type ofstream (i.e. an output file)

MyFile.open("a:\\test.cpp".ios::app);

opens the file text.cpp to add text to the end of the file.

THE IOS COMMANDS

The ios commands are

in		open for reading
out		open for writing
ate		seek end of file
app		append mode - add to end of file
trunc		truncate if file exists
nocreate	open fails if file does not exist
noreplace	open fails if file exists
binary		binary mode (default mode is text)

MyFile.put('q');

Put the character 'q' into the file.

MyFile.close();

Closes the file down.

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cerr

The cerr stream is used to receive error messages. cerr is the standard error stream, corresponding to stderr in the ANSI C library. By default, cerr is assigned to the screen, but it can be redirected.

cerr <<"Run out of memory.\n";

The output from the above will probably go to the screen.

EXERCISE 21

Define a class with only one public variable - an integer. Define a 20 element array of this type. Use a pointer to point at this array. Each time a key is pressed store this character into the array. When the array goes out of scope (i.e. at the end of the file) the keystokes are to be written to a file.

EXERCISE 22

Write a second program to read this file and display the original sequence of keystrokes.

Strings can be stored to files in the same way as any other data type would be written to a file:

#include <iostream.h>
#include <fstream.h>

void main(void)
{
  const int length = 80;
  char name[length];
  char *sptr = name; // sptr has the address of start of name		  		        
                     // string.
  ofstream MyFile;
  cout << "Type a line of text\n";
  cin.getline(name,length,'\n');
  MyFile.open("a:\\stringy.cpp",ios::app);
  while (*sptr != '\0')
  {
    Myfile.put(*sptr++);
  }
  MyFile.close();
}

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PROJECT FILES

So far we have written, compiled and linked one program at a time. The program might have had serveral functions in it, but for the purposes of compilation they were all treated as a single entity. However, it is possible to break a program into separate files, each consisting of one or more functions. These programs can be compiled separately and linked together to form the final executable program.

There now follows a series of separate files. There is only one file with a main function within it.

prjmain.cpp

#include <iostream.h>
#include <conio.h>
/* both of these statements could be in the header file */

#include "a:\cpp\prjhead.h"

/* header file is used to list all the function prototypes in external
   functions to make this file neater */

void main()
{
  clrscr();
  cout << "in prjmain.cpp\n" << endl;
  FuncOne();
  FuncTwo();
}

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All the functions that are not written in pjrmain.cpp need prototypes defining. They can be defined in prjmain.cpp. However, it is neater to define them all in a header file and include the header file..

pjrhead.h

extern void FuncOne();
extern void FuncTwo();

Notice in the following two small code files that header files still need to be included. This is needed for compilation.

prjone.cpp

#include <iostream.h>

void FuncOne()
{
  cout << "in prjone.cpp " << endl;
}

prjtwo.cpp

#include <iostream.h>

void FuncTwo()
{
  cout << "in prjtwo.cpp" << endl;
}

All these files are bound together using a project file.

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HOW TO SET UP A PROJECT FILE

• From the project menu select open project. Since this is your first project file, type the name of your choice (the prj extension will be added automatically). Notice that the project file will be saved to the suggested directory - you may want to select a different drive / directory.
• The project window then opens. You need to list all the files that you will want to link together.
• Select insert. Insert the files and then press done. Notice that any header files written do not need to be included - these are identified from with the code files.
• Each one of the source code files can now be edited and compiled separately.
• To produce the final executable file, compile make is selected. This will compile all the source code files that are out of date (i.e. changed since their last compile) and then link all the compiled object files together.
• The compile build all is the same as the make utitity, but will compile and link regardless of whether they are out of date.

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EXERCISE 23 - THE TELEPHONE BOOK

Define a class with two variables. One a string (to hold a person's name), the other an 11 digit phone number. These must be stored on disc in an ASCII text file called phone.dat.

The member functions of the class should include:

• add a phone number
• access phone number by name
• access name by phone number
• display name and phone number
• print names and numbers

The phone database is created by reading the names from disc into an array in memory.

The whole exercise should be setup as a project using three separate modules:

• header file containing the class declaration
• function file containing the function declarations
• main file containing the program execution.

The telephone number must be verified that it is a number.