Input, Output, and Files

Output with cout

// write.cpp -- use cout.write()

#include <iostream.h>
#include <string.h>

int main(void)
{
	char * state1 = "Ohio";
	char * state2 = "Utah";
	char * state3 = "Euphoria";

	int len = strlen(state2);
	cout << "Increasing loop index:\n";
	for (int i = 1; i <= len; i++)
	{
		cout.write(state2,i);
		cout << "\n";
	}

// concatenate output
	cout << "Decreasing loop index:\n";
	for (i = len; i > 0; i--)
		cout.write(state2,i) << "\n";

// exceed string length
	cout << "Exceeding string length:\n";
	cout.write(state2, len + 5) << "\n";

	return 0;
}



// defaults.cpp -- cout default formats 

#include <iostream.h>

int main(void) 
{
	cout << "12345678901234567890\n";
	char ch = 'K'; 
	int t = 273;
	cout << ch << ":\n";
	cout << t << ":\n";
	cout << -t <<":\n";

	double f1 = 1.200;
	cout << f1 << ":\n";	
	cout << (f1 + 1.0 / 9.0) << ":\n";

	double f2 = 1.67E2;
	cout << f2 << ":\n";
	f2 += 1.0 / 9.0;
	cout << f2 << ":\n";
	cout << (f2 * 1.0e4) << ":\n";


	double f3 = 2.3e-4;
	cout << f3 << ":\n";
	cout << f3 / 10 << ":\n";

	return 0; 
}


// manip.cpp -- using format manipulators

#include <iostream.h>

int main(void)
{
	cout << "Enter an integer: ";
	int n;
	cin >> n;

	cout << "n     n*n\n";
	cout << n << "     " << n * n << " (decimal)\n";
// set to hex mode
	cout << hex;		
	cout << n << "     ";
	cout << n * n << " (hexadecimal)\n";

// set to octal mode
	cout << oct << n << "     " << n * n << " (octal)\n";

// alternative way to call a manipulator
	dec(cout);
	cout << n << "     " << n * n << " (decimal)\n";

	return 0;
}


// width.cpp -- use the width method

#include <iostream.h>

int main(void)
{
	int w = cout.width(30);
	cout << "default field width = " << w << ":\n";

	cout.width(5);
	cout << "N" <<':';
	cout.width(8);
	cout << "N * N" << ":\n";

	for (long i = 1; i <= 100; i *= 10)
	{
		cout.width(5);
		cout << i <<':';
		cout.width(8);
		cout << i * i << ":\n";
	}

	return 0;
}



// fill.cpp -- change fill character for fields

#include <iostream.h>

int main(void)
{
	cout.fill('*');
	char * staff[2] = { "Waldo Whipsnade", "Wilmarie Wooper"};
	long bonus[2] = {900, 1350};

	for (int i = 0; i < 2; i++)
	{
		cout << staff[i] << ": $";
		cout.width(7);
		cout << bonus[i] << "\n";
	}

	return 0;
}



// precise.cpp -- set the precision

#include <iostream.h>

int main(void)
{
	float price1 = 20.40;
	float price2 = 1.9 + 8.0 / 9.0;

	cout << "\"Furry Friends\" is $" << price1 << ".\n";
	cout << "\"Fiery Fiends\" is $" << price2 << ".\n";

	cout.precision(2);
	cout << "\"Furry Friends\" is $" << price1 << ".\n";
	cout << "\"Fiery Fiends\" is $" << price2 << ".\n";

	return 0;
}



// showpt.cpp -- set the precision, show trailing point

#include <iostream.h>

int main(void)
{
	float price1 = 20.40;
	float price2 = 1.9 + 8.0 / 9.0;
	
	cout.setf(ios::showpoint);
	cout << "\"Furry Friends\" is $" << price1 << ".\n";
	cout << "\"Fiery Fiends\" is $" << price2 << ".\n";

	cout.precision(2);
	cout << "\"Furry Friends\" is $" << price1 << ".\n";
	cout << "\"Fiery Fiends\" is $" << price2 << ".\n";

	return 0;
}



// setf.cpp -- use setf() to control formatting

#include <iostream.h>

int main(void)
{
    int temperature = 63;

	cout << "Today's water temperature: ";
    	cout.setf(ios::showpos);	// show plus sign
  	cout << temperature << "\n";

    	cout << "For our programming friends, that's\n";
	cout << hex << temperature << "\n"; // use hex
    	cout.setf(ios::uppercase);	// use uppercase in hex
    	cout.setf(ios::showbase);	// use 0X prefix for hex
	cout << "or\n";
    	cout << temperature << "\n";

    return 0;
}



// setf2.cpp -- use setf() with 2 arguments to control formatting

#include <iostream.h>
#include <math.h>

int main(void)
{
	// use left justification, show the plus sign, show trailing
	// zeros, with a precision of 3
	cout.setf(ios::left, ios::adjustfield);
	cout.setf(ios::showpos);
	cout.setf(ios::showpoint);
	cout.precision(3);
	// use e-notation and save old format setting
	long old = cout.setf(ios::scientific, ios::floatfield);

	cout << "Left Justification:\n";
	for (long n = 1; n <= 41; n+= 10)
	{
		cout.width(4);
		cout << n << "|";
		cout.width(12);
		cout << sqrt(n) << "|\n";
	}

	// change to internal justification
	cout.setf(ios::internal, ios::adjustfield);
	// restore default floating-point display style
	cout.setf(old, ios::floatfield);

	cout << "Internal Justification:\n";
	for (n = 1; n <= 41; n+= 10)
	{
		cout.width(4);
		cout << n << "|";
		cout.width(12);
		cout << sqrt(n) << "|\n";
	}

	// use right justification, fixed notation 
	cout.setf(ios::right, ios::adjustfield);
	cout.setf(ios::fixed, ios::floatfield);
	cout << "Right Justification:\n";
	for (n = 1; n <= 41; n+= 10)
	{
		cout.width(4);
		cout << n << "|";
		cout.width(12);
		cout << sqrt(n) << "|\n";
	}

	return 0;
}



// iomanip.cpp -- use manipulators from iomanip.h

// some systems require explicitly linking the math library
#include <iostream.h>
#include <iomanip.h>
#include <math.h>

int main(void)
{
	cout.setf(ios::showpoint);
	cout.setf(ios::fixed, ios::floatfield);
	cout.setf(ios::right, ios::adjustfield);

	cout << setw(6) << "N" << setw(14) << "square root"
		 << setw(15) << "fourth root\n";

     double root;
	for (int n = 10; n <=100; n += 10)
	{
        root       = sqrt(n);
		cout << setw(6) << n
		       << setw(12) << setprecision(3) << root
		       << setw(14) << setprecision(4) << sqrt(root)
		       << "\n";
	}

	return 0;
}

Input with cin

// check_it.cpp -- validate input

#include <iostream.h>

int main(void)
{
	cout.precision(2);
	cout.setf(ios::showpoint);
	cout.setf(ios::fixed, ios::floatfield);
	cout << "Enter numbers: ";

	double sum = 0.0;
	double input;
	while (cin >> input)
	{
		sum += input;
	}

	cout << "Last value entered = " << input << "\n";
	cout << "Sum = " << sum << "\n";
	return 0;
}



// get_fun.cpp -- using get() and getline()

// note: some C++ inplementations don't support getline ()
#include <iostream.h>

const int Limit = 80;
int main(void)
{
	char input[Limit];

	cout << "Enter a string for getline() processing:\n";
	cin.getline(input, Limit, '#');
	cout << "Here is your input:\n";
	cout << input << "\nDone with phase 1\n";

	char ch;
	cin.get(ch);
	cout << "The next input character is " << ch << "\n";

	if (ch != '\n')
		cin.ignore(Limit, '\n'); 	// discard rest of line

	cout << "Enter a string for get() processing:\n";
	cin.get(input, Limit, '#');
	cout << "Here is your input:\n";
	cout << input << "\nDone with phase 2\n";

	cin.get(ch);
	cout << "The next input character is " << ch << "\n";

	return 0;
}



// peeker.cpp -- some istream methods

#include <iostream.h>
#include <stdlib.h>		// for exit()

int main(void)
{

//  read and echo input up to a # character
    char ch;

	while(cin.get(ch))		// terminates on EOF
	{
	     if (ch != '#')
			cout << ch;
	     else
	     {
			cin.putback(ch);	// reinsert character      			
			break;
	     }
	}

	if (!cout.eof())
	{
	     cin.get(ch);
	     cout << '\n' << ch << " is next input character.\n";
	}
	else
    {
	     cout << "End of file reached.\n";
	     exit(0);
	}

	while(cin.peek() != '#')		// look ahead
	{
	     cin.get(ch);
	     cout << ch;
	}
	cin.get(ch);
	cout << '\n' << ch << " is next input character.\n";

	return 0;
}



// truncate.cpp -- use get() to truncate input line, if necessary

#include <iostream.h>
const int SLEN = 10;
int main(void)
{
	char name[SLEN];
	char title[SLEN];
	cout << "Enter your name: ";
	cin.get(name,SLEN);
	if (cin.peek() != '\n')
		cout << "Sorry, we only have enough room for "
				<< name << endl;
	while (cin.get() != '\n')
		continue;
	cout << "Dear " << name << ", enter your title: \n";
	cin.get(title,SLEN);
	cout << " Name: " << name
		 << "\nTitle: " << title << endl;

	return 0;
}

File Input and Output

// file.cpp -- save to a file

#include <iostream.h>	// not needed for many systems
#include <fstream.h>

int main(void)
{
	char filename[20];

	cout << "Enter name for new file: ";
	cin >> filename;

// create output stream object for new file and call it fout
	ofstream fout(filename);

	fout << "For your eyes only!\n";		// write to file
	cout << "Enter your secret number: ";	// write to screen
	float secret;
	cin >> secret;
	fout << "Your secret number is " << secret << "\n";
	fout.close();			// close file

// create input stream object for new file and call it fin
	ifstream fin(filename);
	cout << "Here are the contents of " << filename << ":\n";
	char ch;
	while (fin.get(ch))		// read character from file and
		cout << ch;		// write it to screen
	cout << "Done\n";

	return 0;
}



// count.cpp -- count characters in a list of files

#include <iostream.h>
#include <fstream.h>
#include <stdlib.h>		// for exit()
// #include <console.h>		// for Macintosh
int main(int argc, char * argv[])
{
	// argc = ccommand(&argv);      // for Macintosh
	if (argc == 1)			// quit if no arguments
	{
	cerr << "Usage: " << argv[0] << " filename[s]\n";
	exit(1);
	}

	ifstream fin;	// open stream
	long count;
	long total = 0;
	char ch;

	for (int file = 1; file < argc; file++)
	{
	fin.open(argv[file]);	// connect stream to argv[file]
	count = 0;
	while (fin.get(ch))
		count++;
	cout << count << " characters in " << argv[file] << "\n";
	total += count;
	fin.close();		// disconnect file
	}
	cout << total << " characters in all files\n";

	return 0;
}


// append.cpp -- append information to a file

#include <iostream.h>
#include <fstream.h>
#include <stdlib.h>		// for exit()

const char * file = "guests1.dat";
const int Len = 40;
int main(void)
{
	char ch;

// show initial contents
	ifstream fin;
	fin.open(file);
	// fin.open(file, ios::in |ios::nocreate); //Symantec, MS VC
	if (fin.good())	// or if (fin)
	{
		cout << "Here are the current contents of the "
			 << file << " file:\n";
		while ((ios &)fin.get(ch))
			cout << ch;
	}
	fin.close();

// add new names
	ofstrea fout(file, ios::out | ios::app);
	if (!fout.good())	// or if (!fin)
	{
		cerr << "Can't open " << file << " file for output.\n";
		exit(1);
    }

	cout << "Enter guest names (enter a blank line to quit):\n";
	char name[Len];
	cin.getline(name, Len);
	while (name[0] != '\0')
    {
		fout << name << "\n";
		cin.getline(name, Len);
	}
	fout.close();

// show revised file
	fin.clear();	// not necessary for some compilers
	fin.open(file);
	if (fin.good())
	{
		cout << "Here are the new contents of the "
			 << file << " file:\n";
		while ((ios &)fin.get(ch))
			cout << ch;
	}
	fin.close();

	return 0;
}



// binary.cpp -- append information to a binary file

#include <iostream.h>	// not required by most systems
#include <fstream.h>
#include <iomanip.h>
#include <stdlib.h>	// for exit()

struct planet
{
	char name[20];	// name of planet
	double population;	// its population
	double g;		// its acceleration of gravity
};

const char * file = "planets.dat";

int main(void)
{
	planet pl;
	cout.setf(ios::fixed, ios::floatfield);
	cout.setf(ios::right, ios::adjustfield);

// show initial contents
	ifstream fin;
	fin.open(file, ios::in |ios::binary);		// binary file
	//NOTE: some systems don't accept the ios::binary mode
	if (fin.good())
	{
	cout << "Here are the current contents of the "
		<< file << " file:\n";
	while (fin.read((char *) &pl, sizeof pl))
        {
		cout << setw(20) << pl.name << ": "
		      << setprecision(0) << setw(12) << pl.population
		      << setprecision(2) << setw(6) << pl.g << "\n";
        }
	}
	fin.close();

// add new data
	ofstream fout(file, ios::out | ios::app | ios::binary);
	//NOTE: some systems don't accept the ios::binary mode
	if (fout.fail())
	{
		cerr << "Can't open " << file << " file for output:\n";
		exit(1);
    }

	cout << "Enter planet name (enter a blank line to quit):\n";
	cin.getline(pl.name, 20);
	while (pl.name[0] != '\0')
    {
		cout << "Enter planetary population: ";
		cin >> pl.population;
		cout << "Enter planet's acceleration of gravity: ";
		cin >> pl.g;
		while (cin.get() != '\n')
			continue;
		fout.write((char *) &pl, sizeof pl);
		cout << "Enter planet name (enter a blank line "
		        "to quit):\n";
		cin.getline(pl.name, 20);
	}
	fout.close();

// show revised file
	fin.clear();	// not required for some implementations, but won't hurt
	fin.open(file, ios::in | ios::binary);
	if (fin.good())
	{
	cout << "Here are the new contents of the "
		<< file << " file:\n";
	while (fin.read((char *) &pl, sizeof pl))
        {
		cout << setw(20) << pl.name << ": "
		      << setprecision(0) << setw(12) << pl.population
		      << setprecision(2) << setw(6) << pl.g << "\n";
        }
	}
	fin.close();

	return 0;
}



// random.cpp -- random access to a binary file

#include <iostream.h>	// not required by most systems
#include <fstream.h>
#include <iomanip.h>
#include <stdlib.h>		// for exit()

struct planet
{
	char name[20];      	// name of planet
	double population;	// its population
	double g;		// its acceleration of gravity
};

const char * file = "planets.dat";

int main(void)
{
	planet pl;
	cout.setf(ios::fixed, ios::floatfield);

// show initial contents
	fstream finout; 			// read and write streams
	finout.open(file,ios::in | ios::out | ios::ate |
				ios::binary);
	//NOTE: Some UNIX systems require omitting | ios::binary
	int ct = 0;
	if (finout.good())
	{
		finout.seekg(0);		// go to beginning
		cout << "Here are the current contents of the "
		      << file << " file:\n";
		while (finout.read((char *) &pl, sizeof pl))
		{
			cout << ct++ << ": " << setw(20) << pl.name << ": "
			<< setprecision(0) << setw(12) << pl.population
			<< setprecision(2) << setw(6) << pl.g << "\n";
		}
		if (finout.eof())
			finout.clear();         // clear eof flag
		else
		{
			cerr << "Error in reading " << file << ".\n";
			exit(1);
		}
	}
	else
	{
		cerr << file << " could not be opened -- bye.\n";
		exit(2);
    }

// change a record
	cout << "Enter the record number you wish to change: ";
	long rec;
	cin >> rec;
	while (cin.get() != '\n')
		continue;     		// get rid of newline
	if (rec < 0 || rec >= ct)
	{
		cerr << "Invalid record number -- bye\n";
		exit(3);
    }
	streampos place = rec * sizeof pl;	// convert to streampos type
	finout.seekg(place);
	if (finout.fail())
	{
		cerr << "Error on attempted seek\n";
		exit(4);
	}

	finout.read((char *) &pl, sizeof pl);
	cout << "Your selection:\n";
	cout << rec << ": " << setw(20) << pl.name << ": "
	<< setprecision(0) << setw(12) << pl.population
	<< setprecision(2) << setw(6) << pl.g << "\n";
    if (finout.eof())
		finout.clear();         		// clear eof flag
	finout.seekp(place);	// go back

	cout << "Enter planet name: ";
	cin.getline(pl.name, 20);
	cout << "Enter planetary population: ";
	cin >> pl.population;
	cout << "Enter planet's acceleration of gravity: ";
	cin >> pl.g;
	finout.write((char *) &pl, sizeof pl) << flush;
	if (finout.fail())
	{
		cerr << "Error on attempted write\n";
		exit(5);
	}

// show revised file
	ct = 0;
	finout.seekg(0);			// go to beginning of file
	cout << "Here are the new contents of the " << file
	     << " file:\n";
	while (finout.read((char *) &pl, sizeof pl))
    {
		cout << ct++ << ": " << setw(20) << pl.name << ": "
		      << setprecision(0) << setw(12) << pl.population
		       << setprecision(2) << setw(6) << pl.g << "\n";
	}
	finout.close();

	return 0;
}


// randomds.cpp -- draft standard random access to a binary file

#include <iostream.h>	// not required by most systems
#include <fstream.h>
#include <stdlib.h>		// for exit()

struct planet
{
	char name[20];      	// name of planet
	double population;	// its population
	double g;		// its acceleration of gravity
};

const char * file = "planet.dat";

int main(void)
{
	planet pl;
	cout.setf(ios::fixed, ios::floatfield);
	cout.setf(ios::right, ios::adjustfield);

// show initial contents
	ios::openmode fmode = ios::in | ios::out | ios::ate | ios::binary;
	ifstream fin(file,fmode);	// associate input stream with a fiel
	ostream fout(fin.rdbuf());	// associate output stream with same file
	streampos end;
	streampos now;
	int ct = 0;
	if (fin.good())
	{	
		end = fin.rdbuf()->pubseekoff(0,ios::end, fmode);	// locate file end
		now = fin.rdbuf()->pubseekoff(0,ios::beg, fmode);	// go to beginning
		cout << "Here are the current contents of the "
			<< file << " file:\n";
		while (now != end)
		{
			fin.read((char *) &pl, sizeof pl);	// read a block
			now = fin.rdbuf()->pubseekoff(0,ios::cur, fmode);
			// now is new location	
			cout << ct++ << ": " ;
			cout.width(20); 
			cout << pl.name << ": ";
			cout.precision(0);
			cout.width(12);
			cout << pl.population;
			cout.precision(2);
			cout.width(6);
			cout << pl.g << "\n";
		}
		if (fin.eof())
			fin.clear();		// clear eof flag
	}
	else
	{
		cerr << file << " could not be opened -- bye.\n";
		exit(2);
	}

// change a record
	cout << "Enter the record number you wish to change: ";
	long rec;
	cin >> rec;  
	while (cin.get() != '\n')
		continue;     		// get rid of newline
	if (rec < 0 || rec >= ct)
	{
		cerr << "Invalid record number -- bye\n";
		exit(3);
	}
	streamoff offset = rec * sizeof pl;
	now = fin.rdbuf()->pubseekoff(offset,ios::beg, fmode);
	if (fin.fail())
	{
		cerr << "Error on attempted seek\n";
		exit(4);
	}

	fin.read((char *) &pl, sizeof pl);
	cout << "Your selection:\n";
	cout << rec << ": ";
	cout.width(20); 
	cout << pl.name << ": ";
	cout.precision(0);
	cout.width(12);
	cout << pl.population;
	cout.precision(2);
	cout.width(6);
	cout << pl.g << "\n";
	if (fin.eof())
		fin.clear();			// clear eof flag

	cout << "Enter planet name: ";
	cin.getline(pl.name, 20);
	cout << "Enter planetary population: ";
	cin >> pl.population;
	cout << "Enter planet's acceleration of gravity: ";
	cin >> pl.g;
	fout.rdbuf()->pubseekoff(offset, ios::beg, fmode);	// go back 
	fout.write((char *) &pl, sizeof pl) << flush;
	if (fout.fail())
	{
		cerr << "Error on attempted write\n";
		exit(5);
	}

// show revised file
	ct = 0;
	now = fin.rdbuf()->pubseekoff(0,ios::beg,fmode);		// go to beginning
	cout << "Here are the new contents of the " << file
		<< " file:\n";
	while (now != end)
    {
		fin.read((char *) &pl, sizeof pl);
		now =fin.rdbuf()->pubseekoff(0, ios::cur, fmode);
		cout << ct++ << ": " ;
		cout.width(20); 
		cout << pl.name << ": ";
		cout.precision(0);
		cout.width(12);
		cout << pl.population;
		cout.precision(2);
		cout.width(6);
		cout << pl.g << "\n";
	}
	fin.close();

	return 0;
}

Incore Formatting

// strout.cpp -- incore formatting (output)

#include <iostream.h>
#include <strstream.h> 
const int LIM = 20;
int main(void)
{
	ostrstream outstr;	// manages a char array
	
	char hdisk[LIM];
	cout << "What's the name of your hard disk? ";
	cin.getline(hdisk, LIM);
	int cap;
	cout << "What's its capacity in MB? ";
	cin >> cap;
	// write formatted information to array
	outstr << "The hard disk " << hdisk << " has a capacity of "
			<< cap << " megabytes.\n";	
	outstr.put('\0');			// make it a string
	char * po = outstr.str();	// get address of array
	cout << po;					// show contents
	delete po;					// free memory
	return 0;
}	



// strin.cpp -- formatted reading from a char array

#include <iostream.h>
#include <strstream.h>
const int LIM = 20;
int main(void)
{
	char buf[] = "It was a dark and stormy day, and "
				 " the full moon glowed brilliantly.";
	istrstream instr(buf, sizeof buf);	// use buf for input
	char word[LIM];
	while ((instr >> word).good())	// read a word a time
		cout << word << endl;
	return 0;
}