C++ Tutorial/Development/cout

An I/O manipulator: cout

<source lang="cpp">#include <iostream>

1. include <iomanip>

using namespace std;

int main() {

 cout << setprecision(2) << 1000.243 << endl; 

 return 0; 

}</source>

1e+003

An I/O manipulator: cout

<source lang="cpp">#include <iostream>

1. include <iomanip>

using namespace std;

int main() {

 cout << setw(20) << "Hello there."; 

 return 0; 

}</source>

Hello there.

Check cout flags

<source lang="cpp">#include<iostream.h> void showflags(); main() {

 showflags();
 cout.setf(ios::oct|ios::showbase|ios::fixed);
 showflags();
 return 0;

} void showflags() {

 long f;
 char flgs[15][12]={
   "skipws",
      "left",
      "right",
      "internal",
      "dec",
      "oct",
      "hex",
      "showbase",
      "showpoint",
      "uppercase",
      "showpos",
      "scientific",
      "fixed",
      "unitbuf",
      "stdio",
 };
 f=cout.flags();
 for(int i=1,j=0;i<0x4000;i=i<<1,j++)
   if(i&f)
        cout<<flgs[j]<<"is on\n";
      else
        cout<<flgs[j]<<"is off\n";
 cout<<"\n";

}</source>

skipwsis off
leftis on
rightis off
internalis off
decis off
octis off
hexis off
showbaseis off
showpointis off
uppercaseis off
showposis off
scientificis off
fixedis on
unitbufis off
skipwsis off
leftis on
rightis on
internalis off
decis off
octis off
hexis on
showbaseis off
showpointis off
uppercaseis on
showposis off
scientificis off
fixedis on
unitbufis off

cout boolalpha: cause bool values to display as true or false

<source lang="cpp">#include <iostream> using std::boolalpha; using std::cout; using std::endl; int main() {

  bool a = true;
  bool b = false;
  cout << boolalpha;
  cout << "a = " << a << "; b = " << b;
  return 0;

}</source>

a = true; b = false

cout: fill()

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 cout.setf(ios::showpos); 
 cout.setf(ios::scientific); 
 cout << 123 << " " << 123.23 << "\n"; 


 cout.fill("#");  // fill using # 
 cout.width(10);  // in a field of 10 characters 
 cout << 123 << " "; 
 cout.width(10);  // set width to 10 
 cout << 123.23; 

 return 0; 

}</source>

+123 +1.232300e+002
######+123 +1.232300e+002

cout: flags() and unsetf()

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 ios::fmtflags f; 

 f = cout.flags(); 

 if(f & ios::showpos) 
   cout << "showpos is set for cout.\n"; 
 else 
   cout << "showpos is cleared for cout.\n"; 

 cout << "\nSetting showpos for cout.\n"; 
 cout.setf(ios::showpos); 

 f = cout.flags(); 

 if(f & ios::showpos) 
   cout << "showpos is set for cout.\n"; 
 else 
   cout << "showpos is cleared for cout.\n"; 

 cout << "\nClearing showpos for cout.\n"; 
 cout.unsetf(ios::showpos); 

 f = cout.flags(); 

 if(f & ios::showpos) 
   cout << "showpos is set for cout.\n"; 
 else 
   cout << "showpos is cleared for cout.\n"; 

 return 0; 

}</source>

showpos is cleared for cout.
Setting showpos for cout.
showpos is set for cout.
Clearing showpos for cout.
showpos is cleared for cout.

cout: precision()

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 cout.setf(ios::showpos); 
 cout.setf(ios::scientific); 
 cout << 123 << " " << 123.23 << "\n"; 

 cout.precision(2); // two digits after decimal point 
 cout.width(10);    // in a field of 10 characters 
 cout << 123 << " "; 
 cout.width(10);    // set width to 10 
 cout << 123.23 << "\n"; 

 return 0; 

}</source>

+123 +1.232300e+002
      +123 +1.23e+002

cout: setf()

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 // Turn on showpos and scientific flags. 
 cout.setf(ios::showpos); 
 cout.setf(ios::scientific); 

 cout << 123 << " " << 123.23 << " "; 

 return 0; 

}</source>

+123 +1.232300e+002

cout.setf(ios::showpoint | ios::showpos, ios::showpoint);

<source lang="cpp">#include <iostream> using namespace std; int main( ) {

 cout.setf(ios::showpoint | ios::showpos, ios::showpoint);
 cout << 100.0;
 return 0;

}</source>

100.000

cout: setiosflags()

<source lang="cpp">#include <iostream>

1. include <iomanip>

using namespace std;

int main() {

 cout << setiosflags(ios::showpos) << setiosflags(ios::scientific) << 123 << 123.23; 

 return 0; 

}</source>

+123 +1.232300e+002

cout: unsetf

<source lang="cpp">#include <iostream.h> main(void) {

 cout.setf(ios::showpos);
 cout.setf(ios::scientific);
 cout << 123 << "  "<< 123.456 << endl;
 cout.precision(3);
 cout.width(10);
 cout << 123 << "  "<< 123.456 << endl;;
 cout.fill("#");
 cout.width(10);
 cout.unsetf(ios::scientific|ios::showpos);
 cout.precision(5);
 cout << 123 << "  " << 123.456;
 return 0;

}</source>

+123  +1.234560e+002
      +123  +1.235e+002
#######123  123.46

cout: width()

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 cout.setf(ios::showpos); 
 cout.setf(ios::scientific); 
 cout << 123 << " " << 123.23 << "\n"; 

 cout.precision(2); // two digits after decimal point 
 cout.width(10);    // in a field of 10 characters 
 cout << 123 << " "; 
 cout.width(10);    // set width to 10 
 cout << 123.23 << "\n"; 

 return 0; 

}</source>

+123 +1.232300e+002
      +123 +1.23e+002

Demonstrating left justification and right justification

<source lang="cpp">#include <iostream> using std::cout; using std::endl; using std::left; using std::right;

1. include <iomanip>

using std::setw; int main() {

  int x = 12345;
  cout << "Default is right justified:" << endl<< setw( 10 ) << x;
  cout << "\n\nUse std::left to left justify x:\n"<< left << setw( 10 ) << x;

  cout << "\n\nUse std::right to right justify x:\n"<< right << setw( 10 ) << x << endl;
  return 0;

}</source>

Default is right justified:
     12345
Use std::left to left justify x:
12345
Use std::right to right justify x:
     12345

Demonstrating stream-manipulators boolalpha and noboolalpha.

<source lang="cpp">#include <iostream> using std::boolalpha; using std::cout; using std::endl; using std::noboolalpha; int main() {

  bool booleanValue = true;
  cout << "booleanValue is " << booleanValue << endl;
  cout << "booleanValue (after using boolalpha) is "<< boolalpha << booleanValue << endl << endl;
  booleanValue = false; // change booleanValue
  cout << noboolalpha << endl; // use noboolalpha
  cout << "booleanValue is " << booleanValue << endl;
  cout << "booleanValue (after using boolalpha) is " << boolalpha << booleanValue << endl;
  return 0;

}</source>

booleanValue is 1
booleanValue (after using boolalpha) is true

booleanValue is 0
booleanValue (after using boolalpha) is false

Demonstrating the flags member function

<source lang="cpp">#include <iostream> using std::cout; using std::endl; using std::ios_base; using std::oct; using std::scientific; using std::showbase; int main() {

  int integerValue = 1000;
  double doubleValue = 0.0947628;
  cout << cout.flags() << "\n\n" << integerValue << "\t" << doubleValue << endl << endl;
  ios_base::fmtflags originalFormat = cout.flags();
  cout << showbase << oct << scientific;
  cout << cout.flags() << "\n\n" << integerValue << "\t" << doubleValue << endl << endl;
  cout.flags( originalFormat );
  cout << cout.flags() << "\n\n" << integerValue << "\t" << doubleValue << endl;
  return 0;

}</source>

4098
1000    0.0947628
011500
01750   9.476280e-002
4098
1000    0.0947628

Fixed-point mode, show a "+" for positive nums, show 3 digits to the right of the decimal

<source lang="cpp">#include <iostream>

1. include <iomanip>
2. include <string>

using namespace std; int main( ) {

  ios_base::fmtflags flags = cout.flags( );
  double pi = 3.14285714;
  cout << "pi = " << fixed            
       << showpos                     
       << setprecision(3)
       << pi << "\n";    
  cout.flags(flags);

}</source>

pi = +3.143

ios::showpos | ios::showbase | ios::oct | ios::right

<source lang="cpp">#include <iostream> using namespace std; void showflags(); int main() {

 // show default condition of format flags
 showflags();
 // showpos, showbase, oct, right are on, others off
 ios::fmtflags f = ios::showpos | ios::showbase | ios::oct | ios::right;
 cout.flags(f);
 showflags();
 return 0;

}

void showflags() {

 ios::fmtflags f;
 long i;
 f = cout.flags(); // get flag settings
 // check each flag
 for(i=0x4000; i; i = i >> 1)
   if(i & f) cout << "1 ";
   else cout << "0 ";
 cout << " \n";

}</source>

0 0 1 0 0 0 0 0 0 0 0 0 0 1 0
0 0 0 1 0 1 0 1 1 0 0 0 0 0 0

OR together two or more flags

<source lang="cpp">#include <iostream> using namespace std; int main() {

 cout.setf(ios::showpoint | ios::showpos);
 cout << 100.0; 
 return 0;

}</source>

+100.000

Output a pointer

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 char *ptr; 

 ptr = "Pointers add power to C++.\n"; 

 cout << ptr; 

 return 0; 

}</source>

Pointers add power to C++.

parameterless manipulators that operate on output streams

<source lang="cpp">Manipulator Purpose boolalpha Turns on boolalpha flag. endl Outputs a newline. ends Outputs a null. dec Turns on dec flag. Turns off the hex and oct flags. fixed Turns on fixed flag. Turns off the scientific flag. flush Flushes the stream. hex Turns on hex flag. Turns off the dec and oct flags. internal Turns on internal flag. Turns off the left and right flags. left Turns on left flag. Turns off the right and internal flags. noboolalpha Turns off boolalpha flag. noshowbase Turns off showbase flag. noshowpoint Turns off showpoint flag. noshowpos Turns off showpos flag. nounitbuf Turns off unitbuf flag. nouppercase Turns off uppercase flag. oct Turns on oct flag. Turns off the dec and hex flags. right Turns on right flag. Turns off the left and internal flags. scientific Turns on scientific flag. Turns off the fixed flag. showbase Turns on showbase flag. showpoint Turns on showpoint flag. showpos Turns on showpos flag. unitbuf Turns on unitbuf flag. uppercase Turns on uppercase flag.

1. include <iostream>

using namespace std; void showflags(void); int main(void) {

  showflags();
  cout.setf(ios::right | ios::showpoint | ios::fixed);
  showflags();

} void showflags(void){

  long flag_set, i;
  int j;
  char flags[15][12] = {
     "skipws", "left", "right", "internal", "dec",
     "oct", "hex", "showbase", "showpoint", "uppercase",
     "showpos", "scientific", "fixed", "unitbuf",
  };
  flag_set = cout.flags();
  for (i=1, j=0; i<0x2000; i = i<<1, j++)
     if (i & flag_set)
        cout << flags[j] << " is on." << endl;
     else
        cout << flags[j] << " is off." << endl;
  cout << endl;

}</source>

Printing a line of text with multiple statements

<source lang="cpp">#include <iostream> int main() {

  std::cout << "Welcome ";
  std::cout << "to C++!\n";
  return 0;

}</source>

Welcome to C++!

Printing an integer with internal spacing and plus sign

<source lang="cpp">#include <iostream> using std::cout; using std::endl; using std::internal; using std::showpos;

1. include <iomanip>

using std::setw; int main() {

  cout << internal << showpos << setw( 10 ) << 123 << endl;
  return 0;

}</source>

+      123

Printing multiple lines of text with a single statement: use the \n

<source lang="cpp">#include <iostream> int main() {

  std::cout << "Welcome\nto\n\nC++!\n";
  return 0;

}</source>

Welcome
to
C++!

Scientific mode; don"t show plus sign anymore

<source lang="cpp">#include <iostream>

1. include <iomanip>
2. include <string>

using namespace std; int main( ) {

  ios_base::fmtflags flags = cout.flags( );
  double pi = 3.14285714;
  cout << "pi = " << scientific
       << noshowpos
       << pi << "\n";
  cout.flags(flags);

}</source>

pi = 3.142857e+000

Set cout to output hex

<source lang="cpp">#include <iostream> using namespace std; int main() {

 cout.setf(ios::hex, ios::basefield);
 cout << 100; // this displays 64
 return 0;

}</source>

64

setiosflags(ios::showpos); and setiosflags(ios::showbase);

<source lang="cpp">#include <iostream>

1. include <iomanip>

using namespace std; int main() {

 cout << setiosflags(ios::showpos);
 cout << setiosflags(ios::showbase);
 cout << 123 << " " << hex << 123;
 return 0;

}</source>

+123 0x7b

Set ios::showpoint, ios::showpos for double pointer number

<source lang="cpp">#include <iostream> using namespace std; int main() {

 cout.setf(ios::showpoint);
 cout.setf(ios::showpos);
 cout << 100.0; 
 return 0;

}</source>

+100.000

Show default condition of format flags

<source lang="cpp">#include <iostream> using namespace std; void showflags() ; int main() {

 showflags();
 cout.setf(ios::right | ios::showpoint | ios::fixed);
 showflags();
 return 0;

} void showflags() {

 ios::fmtflags f;
 long i;
 f = cout.flags(); // get flag settings
 // check each flag
 for(i=0x4000; i; i = i >> 1)
   if(i & f) cout << "1 ";
   else cout << "0 ";
 cout << " \n";

}</source>

0 0 1 0 0 0 0 0 0 0 0 0 0 1 0
0 0 1 0 1 0 0 1 0 0 0 0 1 1 0

Skip leading whitespace.

<source lang="cpp">#include <iostream> using namespace std;

int main() {

 char s[80]; 

 cin >> ws >> s; 
 cout << s; 

 return 0; 

}</source>

string string
string

Stream-manipulator uppercase.

<source lang="cpp">#include <iostream> using std::cout; using std::endl; using std::hex; using std::showbase; using std::uppercase; int main() {

  cout << uppercase << 4.345e10 << endl << hex << showbase << 123456789  << endl;
  return 0;

}</source>

4.345E+010
0X75BCD15

To use a parameterized manipulator, you must include <iomanip>. It defines the following manipulators:

<source lang="cpp">resetiosflags (ios_base::fmtflags f) Turn off the flags specified in f. setbase(int base) Set the number base to base. setfill(int ch) Set the fill character to ch. setiosflags(ios_base::fmtflags f) Turn on the flags specified in f. setprecision (int p) Set the number of digits of precision. setw(int w) Set the field width to w.</source>

unset flag one by one

<source lang="cpp">#include <iostream> using namespace std; int main() {

 cout.setf(ios::uppercase | ios::scientific);
 cout << 100.12;
 cout.unsetf(ios::uppercase);
 cout << " \n" << 100.12;
 return 0;

}</source>

1.001200E+002
1.001200e+002"

Use function in cout statement

<source lang="cpp">#include <iostream> using namespace std; int box(int length, int width, int height); // return the volume int main() {

 // use the return value of box( ) directly 
 cout << "The volume is " <<  box(10.1, 11.2, 3.3); 

 return 0; 

} // This function returns a value. int box(int length, int width, int height) {

 return length * width * height ; 

}</source>

The volume is 330

Use std::cout to output message to console

<source lang="cpp">#include <iostream>

int main()
{
    std::cout << "Hello World!\n";
    return 0;
}</source>

Hello World!

Use std::cout to output various data

<source lang="cpp">#include <iostream> int main() {

   std::cout << "test.\n";
   std::cout << "Here is 5: " << 5 << "\n";
   std::cout << "Here is a very big number:\t" << 70000;
   std::cout << (float) 5/8 << std::endl;
   std::cout << (double) 7000 * 7000 << std::endl;
   std::cout << "a liiiiiiiiiiiiiiiiiiiiiiine\n";
   return 0;

}</source>

test.
Here is 5: 5
Here is a very big number:      700000.625
4.9e+007
a liiiiiiiiiiiiiiiiiiiiiiine

Use std::endl to output a new line sign

<source lang="cpp">#include <iostream> int main() {

 int x = 5;
 int y = 7;
 std::cout << std::endl;
 std::cout << x + y << " " << x * y;
 std::cout << std::endl;
 return 0;

}</source>

12 35

use the setiosflags( ) manipulator to directly set the various format flags related to a stream.

<source lang="cpp">#include <iostream>

1. include <iomanip>

using namespace std;

int main() {

 cout << setiosflags(ios::showpos);
 cout << setiosflags(ios::showbase);
 cout << 123 << " " << hex << 123;
  
 return 0;

}</source>

Using Manipulators to Format I/O

<source lang="cpp">/* Manipulator Purpose Input/Output boolalpha Turns on boolapha flag. Input/Output dec Turns on dec flag. Input/Output endl Output a newline character and flush the stream. Output ends Output a null. Output fixed Turns on fixed flag. Output flush Flush a stream. Output hex Turns on hex flag. Input/Output internal Turns on internal flag. Output left Turns on left flag. Output nobooalpha Turns off boolalpha flag. Input/Output noshowbase Turns off showbase flag. Output noshowpoint Turns off showpoint flag. Output noshowpos Turns off showpos flag. Output noskipws Turns off skipws flag. Input nounitbuf Turns off unitbuf flag. Output nouppercase Turns off uppercase flag. Output oct Turns on oct flag. Input/Output resetiosflags (fmtflags f) Turn off the flags specified in f. Input/Output right Turns on right flag. Output scientific Turns on scientific flag. Output setbase(int base) Set the number base to base. Input/Output setfill(int ch) Set the fill character to ch. Output setiosflags(fmtflags f) Turn on the flags specified in f. Input/output setprecision (int p) Set the number of digits of precision. Output setw(int w) Set the field width to w. Output showbase Turns on showbase flag. Output showpoint Turns on showpoint flag. Output showpos Turns on showpos flag. Output skipws Turns on skipws flag. Input unitbuf Turns on unitbuf flag. Output uppercase Turns on uppercase flag. Output ws Skip leading white space. Input

• /

1. include <iostream>
2. include <iomanip>

using namespace std;

int main() {

 cout << hex << 100 << endl;
  
 cout << setfill("?") << setw(10) << 2343.0;
  
 return 0;

}</source>

Using showpoint to control the printing of trailing zeros anddecimal points for doubles

<source lang="cpp">#include <iostream> using std::cout; using std::endl; using std::showpoint; int main() {

  cout << "Before using showpoint" << endl
     << "9.9900 prints as: " << 9.9900 << endl
     << "9.9000 prints as: " << 9.9000 << endl
     << "9.0000 prints as: " << 9.0000 << endl << endl;
  cout << showpoint  
     << "After using showpoint" << endl
     << "9.9900 prints as: " << 9.9900 << endl
     << "9.9000 prints as: " << 9.9000 << endl
     << "9.0000 prints as: " << 9.0000 << endl;
  return 0;

}</source>

Before using showpoint
9.9900 prints as: 9.99
9.9000 prints as: 9.9
9.0000 prints as: 9
After using showpoint
9.9900 prints as: 9.99000
9.9000 prints as: 9.90000
9.0000 prints as: 9.00000

Using stream-manipulator showbase to show number base

<source lang="cpp">#include <iostream> using std::cout; using std::endl; using std::hex; using std::oct; using std::showbase; int main() {

  int x = 100;
  cout << "Printing integers preceded by their base:" << endl << showbase;
  cout << x << endl; // print decimal value
  cout << oct << x << endl; // print octal value
  cout << hex << x << endl; // print hexadecimal value
  return 0;

}</source>

Printing integers preceded by their base:
100
0144
0x64

Using write().

<source lang="cpp">#include <iostream>

1. include <string.h>

using namespace std; int main() {

  char One[] = "this is a test";
  int fullLength = strlen(One);
  int tooShort = fullLength -4;
  int tooLong = fullLength + 6;
  cout.write(One,fullLength) << "\n";
  cout.write(One,tooShort) << "\n";
  cout.write(One,tooLong) << "\n";
  return 0;

}</source>