【C++】setw函数的用法和作用【原创技术】

作用：

setw(4)是定义字段长度的函数

用法：

//题目：结构体成员变量

//作者：武叶

//创作时间：2012年4月21日

//使用语言：C++

#include"iostream.h"

#include"iomanip.h"

struct student

{

int num;

char name[20];

char sex;

int age;

}stu={97001,"lin lin",'F',19};

void main()

{

cout<<setw(7)<<stu.num<<setw(20)<<stu.name<<setw(3)<<stu.sex<<setw(3)<<stu.age;

}

先调用#include"iomanip.h"

才能使用setw函数定义字段长度

这是iomanip.h的头文件内容：

/***

*iomanip.h - definitions/declarations for iostream's parameterized manipulators

*

* Copyright (c) 1991-1997, Microsoft Corporation. All rights reserved.

*

*Purpose:

* This file defines the classes, values, macros, and functions

* used by the iostream classes' paramterized manipulators.

* [AT&T C++]

*

* [Public]

*

****/

#if _MSC_VER > 1000

#pragma once

#endif

#ifdef __cplusplus

#ifndef _INC_IOMANIP

#define _INC_IOMANIP

#if !defined(_WIN32) && !defined(_MAC)

#error ERROR: Only Mac or Win32 targets supported!

#endif

#ifdef _MSC_VER

// Currently, all MS C compilers for Win32 platforms default to 8 byte

// alignment.

#pragma pack(push,8)

#include <useoldio.h>

#endif // _MSC_VER

#include <iostream.h>

#ifdef _MSC_VER

#pragma warning(disable:4514) // disable unwanted /W4 warning

// #pragma warning(default:4514) // use this to reenable, if necessary

#endif // _MSC_VER

// #define __MKMANIP(X) \#define X##(T) __##X##_ \#\# T

// __MKMANIP(SMANIP);

// __MKMANIP(SAPP);

// __MKMANIP(IMANIP);

// __MKMANIP(IAPP);

// __MKMANIP(OMANIP);

// __MKMANIP(OAPP);

// __MKMANIP(IOMANIP);

// __MKMANIP(IOAPP);

#define SMANIP(T) __SMANIP_##T

#define SAPP(T) __SAPP_##T

#define IMANIP(T) __IMANIP_##T

#define IAPP(T) __IAPP_##T

#define OMANIP(T) __OMANIP_##T

#define OAPP(T) __OAPP_##T

#define IOMANIP(T) __IOMANIP_##T

#define IOAPP(T) __IOAPP_##T

#define IOMANIPdeclare(T) \

class SMANIP(T) { \

public: \

SMANIP(T)(ios& (*f)(ios&,T), T t) : _fp(f), _tp(t) {} \

friend istream& operator>>(istream& s, const SMANIP(T) & sm) { (*(sm._fp))(s,sm._tp); return s; } \

friend ostream& operator<<(ostream& s, const SMANIP(T) & sm) { (*(sm._fp))(s,sm._tp); return s; } \

private: \

ios& (* _fp)(ios&,T); \

T _tp; \

}; \

class SAPP(T) { \

public: \

SAPP(T)( ios& (*f)(ios&,T)) : _fp(f) {} \

SMANIP(T) operator()(T t) { return SMANIP(T)(_fp,t); } \

private: \

ios& (* _fp)(ios&,T); \

}; \

class IMANIP(T) { \

public: \

IMANIP(T)(istream& (*f)(istream&,T), T t) : _fp(f), _tp(t) {} \

friend istream& operator>>(istream& s, IMANIP(T) & sm) { (*sm._fp)(s,sm._tp); return s; } \

private: \

istream& (* _fp)(istream&,T); \

T _tp; \

}; \

class IAPP(T) { \

public: \

IAPP(T)( istream& (*f)(istream&,T)) : _fp(f) {} \

IMANIP(T) operator()(T t) { return IMANIP(T)(_fp,t); } \

private: \

istream& (* _fp)(istream&,T); \

}; \

class OMANIP(T) { \

public: \

OMANIP(T)(ostream& (*f)(ostream&,T), T t) : _fp(f), _tp(t) {} \

friend ostream& operator<<(ostream& s, OMANIP(T) & sm) { (*sm._fp)(s,sm._tp); return s; } \

private: \

ostream& (* _fp)(ostream&,T); \

T _tp; \

}; \

class OAPP(T) { \

public: \

OAPP(T)(ostream& (*f)(ostream&,T)) : _fp(f) {} \

OMANIP(T) operator()(T t) { return OMANIP(T)(_fp,t); } \

private: \

ostream& (* _fp)(ostream&,T); \

}; \

\

class IOMANIP(T) { \

public: \

IOMANIP(T)(iostream& (*f)(iostream&,T), T t) : _fp(f), _tp(t) {} \

friend istream& operator>>(iostream& s, IOMANIP(T) & sm) { (*sm._fp)(s,sm._tp); return s; } \

friend ostream& operator<<(iostream& s, IOMANIP(T) & sm) { (*sm._fp)(s,sm._tp); return s; } \

private: \

iostream& (* _fp)(iostream&,T); \

T _tp; \

}; \

class IOAPP(T) { \

public: \

IOAPP(T)( iostream& (*f)(iostream&,T)) : _fp(f) {} \

IOMANIP(T) operator()(T t) { return IOMANIP(T)(_fp,t); } \

private: \

iostream& (* _fp)(iostream&,T); \

}; \

IOMANIPdeclare(int)

IOMANIPdeclare(long)

inline ios& __resetiosflags(ios& s, long _flg) { s.setf(0,_flg); return s; }

inline ios& __setfill(ios& s, int _fc) { s.fill((char)_fc); return s; }

inline ios& __setiosflags(ios& s, long _flg) { s.setf(_flg); return s; }

inline ios& __setprecision(ios& s, int _pre) { s.precision(_pre); return s; }

inline ios& __setw(ios& s, int _wid) { s.width(_wid); return s; }

inline SMANIP(long) resetiosflags(long _l) { return SMANIP(long)(__resetiosflags, _l); }

inline SMANIP(int) setfill(int _m) {return SMANIP(int)(__setfill, _m); }

inline SMANIP(long) setiosflags(long _l) {return SMANIP(long)(__setiosflags, _l); }

inline SMANIP(int) setprecision(int _p) {return SMANIP(int)(__setprecision, _p); }

inline SMANIP(int) setw(int _w) { return SMANIP(int)(__setw, _w); }

// Restore previous packing

#ifdef _MSC_VER

#pragma pack(pop)

#endif // _MSC_VER

#endif // _INC_IOMANIP

#endif /* __cplusplus */

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