Question

#include <iomanip>代表什么头文件的？

Answer 1

ctype是一系列和类型有关的头文件，比如isdigit() isxdigit isupper() 等等
iomanip.h是常见与iostream配合使用的，比如控制流输出的函数：setw，left，right等等，如果使用要
using namespace std;

Answer 2

Standard C++ Library Reference
setw
See Also Example
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Specifies the width of the display field.

T6 setw(
streamsize _Wide
);

Parameters
_Wide
The width of the display field.

Return Value
The manipulator returns an object that, when extracted from or inserted into the stream str, calls str.width(_Wide), then returns str.

Example
Copy Code
// iomanip_setw.cpp
// compile with: /EHsc
// Defines the entry point for the console application.
//
// Sample use of the following manipulators:
// resetiosflags
// setiosflags
// setbase
// setfill
// setprecision
// setw

#include <iostream>
#include <iomanip>

using namespace std;

const double d1 = 1.23456789;
const double d2 = 12.3456789;
const double d3 = 123.456789;
const double d4 = 1234.56789;
const double d5 = 12345.6789;
const long l1 = 16;
const long l2 = 256;
const long l3 = 1024;
const long l4 = 4096;
const long l5 = 65536;
int base = 10;

void DisplayDefault( )
{
cout << endl << "default display" << endl;
cout << "d1 = " << d1 << endl;
cout << "d2 = " << d2 << endl;
cout << "d3 = " << d3 << endl;
cout << "d4 = " << d4 << endl;
cout << "d5 = " << d5 << endl;
}

void DisplayWidth( int n )
{
cout << endl << "fixed width display set to " << n << ".\n";
cout << "d1 = " << setw(n) << d1 << endl;
cout << "d2 = " << setw(n) << d2 << endl;
cout << "d3 = " << setw(n) << d3 << endl;
cout << "d4 = " << setw(n) << d4 << endl;
cout << "d5 = " << setw(n) << d5 << endl;
}

void DisplayLongs( )
{
cout << setbase(10);
cout << endl << "setbase(" << base << ")" << endl;
cout << setbase(base);
cout << "l1 = " << l1 << endl;
cout << "l2 = " << l2 << endl;
cout << "l3 = " << l3 << endl;
cout << "l4 = " << l4 << endl;
cout << "l5 = " << l5 << endl;
}

int main( int argc, char* argv[] )
{
DisplayDefault( );

cout << endl << "setprecision(" << 3 << ")" << setprecision(3);
DisplayDefault( );

cout << endl << "setprecision(" << 12 << ")" << setprecision(12);
DisplayDefault( );

cout << setiosflags(ios_base::scientific);
cout << endl << "setiosflags(" << ios_base::scientific << ")";
DisplayDefault( );

cout << resetiosflags(ios_base::scientific);
cout << endl << "resetiosflags(" << ios_base::scientific << ")";
DisplayDefault( );

cout << endl << "setfill('" << 'S' << "')" << setfill('S');
DisplayWidth(15);
DisplayDefault( );

cout << endl << "setfill('" << ' ' << "')" << setfill(' ');
DisplayWidth(15);
DisplayDefault( );

cout << endl << "setprecision(" << 8 << ")" << setprecision(8);
DisplayWidth(10);
DisplayDefault( );

base = 16;
DisplayLongs( );

base = 8;
DisplayLongs( );

base = 10;
DisplayLongs( );

return 0;
}

Output

default display
d1 = 1.23457
d2 = 12.3457
d3 = 123.457
d4 = 1234.57
d5 = 12345.7

setprecision(3)
default display
d1 = 1.23
d2 = 12.3
d3 = 123
d4 = 1.23e+003
d5 = 1.23e+004

setprecision(12)
default display
d1 = 1.23456789
d2 = 12.3456789
d3 = 123.456789
d4 = 1234.56789
d5 = 12345.6789

setiosflags(4096)
default display
d1 = 1.234567890000e+000
d2 = 1.234567890000e+001
d3 = 1.234567890000e+002
d4 = 1.234567890000e+003
d5 = 1.234567890000e+004

resetiosflags(4096)
default display
d1 = 1.23456789
d2 = 12.3456789
d3 = 123.456789
d4 = 1234.56789
d5 = 12345.6789

setfill('S')
fixed width display set to 15.
d1 = SSSSS1.23456789
d2 = SSSSS12.3456789
d3 = SSSSS123.456789
d4 = SSSSS1234.56789
d5 = SSSSS12345.6789

default display
d1 = 1.23456789
d2 = 12.3456789
d3 = 123.456789
d4 = 1234.56789
d5 = 12345.6789

setfill(' ')
fixed width display set to 15.
d1 = 1.23456789
d2 = 12.3456789
d3 = 123.456789
d4 = 1234.56789
d5 = 12345.6789

default display
d1 = 1.23456789
d2 = 12.3456789
d3 = 123.456789
d4 = 1234.56789
d5 = 12345.6789

setprecision(8)
fixed width display set to 10.
d1 = 1.2345679
d2 = 12.345679
d3 = 123.45679
d4 = 1234.5679
d5 = 12345.679

default display
d1 = 1.2345679
d2 = 12.345679
d3 = 123.45679
d4 = 1234.5679
d5 = 12345.679

setbase(16)
l1 = 10
l2 = 100
l3 = 400
l4 = 1000
l5 = 10000

setbase(8)
l1 = 20
l2 = 400
l3 = 2000
l4 = 10000
l5 = 200000

setbase(10)
l1 = 16
l2 = 256
l3 = 1024
l4 = 4096
l5 = 65536

Requirements
Header: <iomanip>

See Also
Reference
iostream Programming
iostreams Conventions

Other Resources
<iomanip> Members

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