Просмотр исходного текста страницы C++ Tutorial/Development/cout

==An I/O manipulator: cout ==


   
<source lang="cpp">#include <iostream> 
#include <iomanip> 
using namespace std; 
 
int main() 
{ 
  cout << setprecision(2) << 1000.243 << endl; 
 
  return 0; 
}</source>
<pre class=codeResult>1e+003</pre>

==An I/O manipulator: cout ==


   
<source lang="cpp">#include <iostream> 
#include <iomanip> 
using namespace std; 
 
int main() 
{ 
  cout << setw(20) << "Hello there."; 
 
  return 0; 
}</source>
<pre class=codeResult>Hello there.</pre>

==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>
<pre class=codeResult>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</pre>

==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>
<pre class=codeResult>a = true; b = false</pre>

==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>
<pre class=codeResult>+123 +1.232300e+002
######+123 +1.232300e+002</pre>

==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>
<pre class=codeResult>showpos is cleared for cout.
Setting showpos for cout.
showpos is set for cout.
Clearing showpos for cout.
showpos is cleared for cout.</pre>

==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>
<pre class=codeResult>+123 +1.232300e+002
      +123 +1.23e+002</pre>

==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>
<pre class=codeResult>+123 +1.232300e+002</pre>

==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>
<pre class=codeResult>100.000</pre>

==cout: setiosflags()==


   
<source lang="cpp">#include <iostream> 
#include <iomanip> 
using namespace std; 
 
int main() 
{ 
  cout << setiosflags(ios::showpos) << setiosflags(ios::scientific) << 123 << 123.23; 
 
  return 0; 
}</source>
<pre class=codeResult>+123 +1.232300e+002</pre>

==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>
<pre class=codeResult>+123  +1.234560e+002
      +123  +1.235e+002
#######123  123.46</pre>

==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>
<pre class=codeResult>+123 +1.232300e+002
      +123 +1.23e+002</pre>

==Demonstrating left justification and right justification==


   
<source lang="cpp">#include <iostream>
using std::cout;
using std::endl;
using std::left;
using std::right;
#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>
<pre class=codeResult>Default is right justified:
     12345
Use std::left to left justify x:
12345
Use std::right to right justify x:
     12345</pre>

==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>
<pre class=codeResult>booleanValue is 1
booleanValue (after using boolalpha) is true

booleanValue is 0
booleanValue (after using boolalpha) is false</pre>

==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>
<pre class=codeResult>4098
1000    0.0947628
011500
01750   9.476280e-002
4098
1000    0.0947628</pre>

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


   
<source lang="cpp">#include <iostream>
#include <iomanip>
#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>
<pre class=codeResult>pi = +3.143</pre>

==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>
<pre class=codeResult>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</pre>

==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>
<pre class=codeResult>+100.000</pre>

==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>
<pre class=codeResult>Pointers add power to C++.</pre>

==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.
   
#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>
<pre class=codeResult>Welcome to C++!</pre>

==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;
#include <iomanip>
using std::setw;
int main()
{
   cout << internal << showpos << setw( 10 ) << 123 << endl;
   return 0;
}</source>
<pre class=codeResult>+      123</pre>

==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>
<pre class=codeResult>Welcome
to
C++!</pre>

==Scientific mode; don"t show plus sign anymore==


   
<source lang="cpp">#include <iostream>
#include <iomanip>
#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>
<pre class=codeResult>pi = 3.142857e+000</pre>

==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>
<pre class=codeResult>64</pre>

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


   
<source lang="cpp">#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
  cout << setiosflags(ios::showpos);
  cout << setiosflags(ios::showbase);
  cout << 123 << " " << hex << 123;
  return 0;
}</source>
<pre class=codeResult>+123 0x7b</pre>

==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>
<pre class=codeResult>+100.000</pre>

==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>
<pre class=codeResult>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</pre>

==Skip leading whitespace.==


   
<source lang="cpp">#include <iostream> 
using namespace std; 
 
int main() 
{ 
  char s[80]; 
 
  cin >> ws >> s; 
  cout << s; 
 
  return 0; 
}</source>
<pre class=codeResult>string string
string</pre>

==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>
<pre class=codeResult>4.345E+010
0X75BCD15</pre>

==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>
<pre class=codeResult>1.001200E+002
1.001200e+002"</pre>

==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>
<pre class=codeResult>The volume is 330</pre>

==Use std::cout to output message to console==


   
<source lang="cpp">#include <iostream>
 int main()
 {
     std::cout << "Hello World!\n";
     return 0;
 }</source>
<pre class=codeResult>Hello World!</pre>

==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>
<pre class=codeResult>test.
Here is 5: 5
Here is a very big number:      700000.625
4.9e+007
a liiiiiiiiiiiiiiiiiiiiiiine</pre>

==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>
<pre class=codeResult>12 35</pre>

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


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

#include <iostream>
#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>
<pre class=codeResult>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</pre>

==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>
<pre class=codeResult>Printing integers preceded by their base:
100
0144
0x64</pre>

==Using write().==


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