INFSY 307C++

Powerpoint 6File I/O

Stream and File I/O

Function Overloading

Files

It is much easier to store large quantities of data on a disk.

We can review data stored on a disk because it remains thereeven after the program has ended.

External Files

Streams: Interface between program and a device

These are a sequence of characters or bytes and have no fixed length; i.e. a data stream

We have used predefined streams:

<iostream.h> cin cout cerr

File I/O

(files are attached to streams)

ifstream - input ofstream - output fstream -input and

output

*These need the header file, <fstream.h>

Part I

Open a workspace called mathio Open a file – call it mathio.h Create a class called mathio and make its

base class be missapp.h Write a function prototype for

open_input_file (). Make it void with no arguments.

Part I (Continued)

Insert #include <fstream.h> at the top of the file.

Insert ifstream ifs; in private.

How to Proceed

1. Associate file with your program:

#define <filename> “external file”

#define infile “test.dat”#define outfile “test. out”

2. Or have the user input a file name to associate file with your program:

cin>>infile; cin>>outfile;

infile [ ] is equal to “test.dat”outfile [ ] is equal to “test. out”

How to Proceed

3. Link a type to a stream

ifstream ifs; //associate ifs with the input // streamofstream ofs;//associate ofs with the output //stream

Remember: #include <fstream.h>

How to Proceed

3. In a function, open the file:

ifs.open (infile);

ofs.open (outfile);

Alternatively, you could combine the definitionand open (as per Savitch text)

ifs.open(“math.dat”);

note: in this case, you still must associate ifs with ifstream

ifstream ifs; //associate ifs with the input // stream

How to Proceed

4. Check to see that your file opened (closed) successfully

if (ifs.fail()) { cerr<<“**Error on Open: ”<<infile<<endl; cout<<“Press any key to exit program”<<endl; system (“pause”); return EXIT_FAILURE; }

*note: 1) <stdlib.h> for EXIT_FAILURE to be recognized 2) exit (1) is also acceptable

int mathio::open_input_file (){ char infile [26]; cout<<“Enter a filename: “<<endl; cin>>infile; ifs.open(infile); if (ifs.fail()) { cerr<<“**Error on Open: ”<<infile<<endl; cout<<“Press any key to exit program”<<endl; system (“pause”); return EXIT_FAILURE; } else return 0;}

How to Proceed

EXIT_FAILURE: is symbolic of an unsuccessful open (note: Savitch uses exit (1) to exit program)

EXIT_SUCCESS:is symbolic of a successful open

<stdlib.h> is needed

How to Proceed

5. Close your file

ifs.close ();ofs.close ();

C++ Statements related to file processing

ifs.get (achar);

ofs.put (achar);

void missapp::read_and_clean (int i, ifstream& ifs, double& digit){char next; char digit_str [15]; int n=0, flag=1;ifs.get (next);while (n < i && next != '\n' && !ifs.eof()){ if (isdigit(next)) { digit_str [n] = next; n++;} else { n++; flag=0; } if (n<i) ifs.get (next); } if (flag ==0) digit=-1; else { digit_str [n]= '\0'; digit=(atof(digit_str)) / 100; } return;}

It is always wise to read everything in as characters

End of line becomes critical to success

void missapp::read_to_endline(ifstream& ifs){

char next;next=' ';while ((next != '\n')&&(!ifs.eof())){ ifs.get(next);} return;

}

Report Processing

You may use formatting commands with any output stream

Example:

ofs.setf(ios::fixed); //i.e. no e notation for //floating point numbers ofs.setf(ios::showpoint) ; //show decimal point and //trailing 0’s ifs.precision (2);

Formatting I/O

• May use screen style stream operators with file processing commands.• Reports are the best way to use such commands.• There needs to be no validation on output! Therefore, printing one character at a time is not necessary. ofs>>n1<<“ “<<n2<<endl; //note the output file //identifier is used instead //of cout

void mathio::output_to_report_file (){ astericks (78); //assume you change astericks //to write a report ofs<<setw (5)<<“”<<setw (25)<<s.first_name<<setw(25)<<s.last_name; ofs <<setw(4)<<letter_grade<<endl; astericks (78); return;}

Sample output_to_report_file ()

Function Overloading

//FILE:missapp.h#ifndef MISSAPP_H_#define MISSAP_H_#include <iostream.h>#include <fstream.h>#include <stdlib.h>#include <ctype.h>class missapp{ public: void read_and_clean (int, ifstream&, double&); void read_and_clean (int, ifstream&, int&); void read_and_clean (int, ifstream&, char []); void read_to_endline (ifstream&); int read_convert_chars (char thename [], int size); int read_convert_to_int (); private: int flag;}; #endif //MISSAPP_H_

Function Overloading

Function Overloading is the ability to declare functions of the samename with different sets of parameters

1) C++ selects the function by examining a) number of arguments b) types of the argument variables c) order of the arguements 2) Used to create several functions with the same name that perform a similar task but with different data types 3) Improves program readability for closely related tasks

Function OverloadingExample

void sum (int j){ j +=5; cout<<j<<endl; return;}

void sum(float j){ j+=5; cout<<j<<endl; return;}

Function Overloadingmain example

void main ( j){ void sum (int ); void sum (float); int x = 5; float y = 3.5 sum (x); sum (y); return;}