C++ Tutorial/Development/cout
Версия от 14:21, 25 мая 2010; (обсуждение)
Содержание
- 1 An I/O manipulator: cout
- 2 An I/O manipulator: cout
- 3 Check cout flags
- 4 cout boolalpha: cause bool values to display as true or false
- 5 cout: fill()
- 6 cout: flags() and unsetf()
- 7 cout: precision()
- 8 cout: setf()
- 9 cout.setf(ios::showpoint | ios::showpos, ios::showpoint);
- 10 cout: setiosflags()
- 11 cout: unsetf
- 12 cout: width()
- 13 Demonstrating left justification and right justification
- 14 Demonstrating stream-manipulators boolalpha and noboolalpha.
- 15 Demonstrating the flags member function
- 16 Fixed-point mode, show a "+" for positive nums, show 3 digits to the right of the decimal
- 17 ios::showpos | ios::showbase | ios::oct | ios::right
- 18 OR together two or more flags
- 19 Output a pointer
- 20 parameterless manipulators that operate on output streams
- 21 Printing a line of text with multiple statements
- 22 Printing an integer with internal spacing and plus sign
- 23 Printing multiple lines of text with a single statement: use the \n
- 24 Scientific mode; don"t show plus sign anymore
- 25 Set cout to output hex
- 26 setiosflags(ios::showpos); and setiosflags(ios::showbase);
- 27 Set ios::showpoint, ios::showpos for double pointer number
- 28 Show default condition of format flags
- 29 Skip leading whitespace.
- 30 Stream-manipulator uppercase.
- 31 To use a parameterized manipulator, you must include <iomanip>. It defines the following manipulators:
- 32 unset flag one by one
- 33 Use function in cout statement
- 34 Use std::cout to output message to console
- 35 Use std::cout to output various data
- 36 Use std::endl to output a new line sign
- 37 use the setiosflags( ) manipulator to directly set the various format flags related to a stream.
- 38 Using Manipulators to Format I/O
- 39 Using showpoint to control the printing of trailing zeros anddecimal points for doubles
- 40 Using stream-manipulator showbase to show number base
- 41 Using write().
An I/O manipulator: cout
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
cout << setprecision(2) << 1000.243 << endl;
return 0;
}1e+003
An I/O manipulator: cout
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
cout << setw(20) << "Hello there.";
return 0;
}Hello there.
Check cout flags
#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";
}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
#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;
}a = true; b = false
cout: fill()
#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;
}+123 +1.232300e+002 ######+123 +1.232300e+002
cout: flags() and unsetf()
#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;
}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()
#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;
}+123 +1.232300e+002
+123 +1.23e+002
cout: setf()
#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;
}+123 +1.232300e+002
cout.setf(ios::showpoint | ios::showpos, ios::showpoint);
#include <iostream>
using namespace std;
int main( )
{
cout.setf(ios::showpoint | ios::showpos, ios::showpoint);
cout << 100.0;
return 0;
}100.000
cout: setiosflags()
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
cout << setiosflags(ios::showpos) << setiosflags(ios::scientific) << 123 << 123.23;
return 0;
}+123 +1.232300e+002
cout: unsetf
#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;
}+123 +1.234560e+002
+123 +1.235e+002
#######123 123.46
cout: width()
#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;
}+123 +1.232300e+002
+123 +1.23e+002
Demonstrating left justification and right justification
#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;
}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.
#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;
}booleanValue is 1 booleanValue (after using boolalpha) is true booleanValue is 0 booleanValue (after using boolalpha) is false
Demonstrating the flags member function
#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;
}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
#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);
}pi = +3.143
ios::showpos | ios::showbase | ios::oct | ios::right
#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";
}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
#include <iostream>
using namespace std;
int main()
{
cout.setf(ios::showpoint | ios::showpos);
cout << 100.0;
return 0;
}+100.000
Output a pointer
#include <iostream>
using namespace std;
int main()
{
char *ptr;
ptr = "Pointers add power to C++.\n";
cout << ptr;
return 0;
}Pointers add power to C++.
parameterless manipulators that operate on output streams
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;
}Printing a line of text with multiple statements
#include <iostream>
int main()
{
std::cout << "Welcome ";
std::cout << "to C++!\n";
return 0;
}Welcome to C++!
Printing an integer with internal spacing and plus sign
#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;
}+ 123
Printing multiple lines of text with a single statement: use the \n
#include <iostream>
int main()
{
std::cout << "Welcome\nto\n\nC++!\n";
return 0;
}Welcome to C++!
Scientific mode; don"t show plus sign anymore
#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);
}pi = 3.142857e+000
Set cout to output hex
#include <iostream>
using namespace std;
int main()
{
cout.setf(ios::hex, ios::basefield);
cout << 100; // this displays 64
return 0;
}64
setiosflags(ios::showpos); and setiosflags(ios::showbase);
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
cout << setiosflags(ios::showpos);
cout << setiosflags(ios::showbase);
cout << 123 << " " << hex << 123;
return 0;
}+123 0x7b
Set ios::showpoint, ios::showpos for double pointer number
#include <iostream>
using namespace std;
int main()
{
cout.setf(ios::showpoint);
cout.setf(ios::showpos);
cout << 100.0;
return 0;
}+100.000
Show default condition of format flags
#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";
}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.
#include <iostream>
using namespace std;
int main()
{
char s[80];
cin >> ws >> s;
cout << s;
return 0;
}string string string
Stream-manipulator uppercase.
#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;
}4.345E+010 0X75BCD15
To use a parameterized manipulator, you must include <iomanip>. It defines the following manipulators:
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.unset flag one by one
#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;
}1.001200E+002 1.001200e+002"
Use function in cout statement
#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 ;
}The volume is 330
Use std::cout to output message to console
#include <iostream>
int main()
{
std::cout << "Hello World!\n";
return 0;
}Hello World!
Use std::cout to output various data
#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;
}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
#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;
}12 35
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
cout << setiosflags(ios::showpos);
cout << setiosflags(ios::showbase);
cout << 123 << " " << hex << 123;
return 0;
}Using Manipulators to Format I/O
/*
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;
}Using showpoint to control the printing of trailing zeros anddecimal points for doubles
#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;
}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
#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;
}Printing integers preceded by their base: 100 0144 0x64
Using write().
#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;
}