作者:gzshun. 原创作品,转载请标明出处!
来源:http://blog.csdn.net/gzshun
在C++输入输出流控制中,就把话语权交给iomanip吧。
以下列出一些比较常用的设置方法:
包含头文件:#include <iomanip>
dec 十进制 dec(c++) == %d(c)
hex 十六进制 oct(c++) == %o(c)
oct 八进制 hex(c++) == %x(c)
setfill(c) 填充字符为c
setprecision(n) 设置n个有效数字
setw(n) 设输出的宽度为n
setiosflags(ios::fixed) 固定输出小数点个数
setiosflags(ios::scientific) 输出指数
setiosflags(ios::left) 左对齐
setiosflags(ios::right) 右对齐
setiosflags(ios::skipws 忽略前导空白
setiosflags(ios::uppercase) 16进制数大写输出
setiosflags(ios::lowercase) 16进制小写输出
setiosflags(ios::showpoint) 强制显示小数点
setiosflags(ios::showpos) 强制显示符号(+/-)
在设置mask有两个方法:setiosflags和setf。
这些用法看头文件就很清楚了,主要在:ios_base.h和iomanip中。
ios_base.h:
/**
* @brief Access to format flags.
* @return The format control flags for both input and output.
*/
fmtflags
flags() const
{ return _M_flags; }
/**
* @brief Setting new format flags all at once.
* @param fmtfl The new flags to set.
* @return The previous format control flags.
*
* This function overwrites all the format flags with @a fmtfl.
*/
fmtflags
flags(fmtflags __fmtfl)
{
fmtflags __old = _M_flags;
_M_flags = __fmtfl;
return __old;
}
/**
* @brief Setting new format flags.
* @param fmtfl Additional flags to set.
* @return The previous format control flags.
*
* This function sets additional flags in format control. Flags that
* were previously set remain set.
*/
fmtflags
setf(fmtflags __fmtfl)
{
fmtflags __old = _M_flags;
_M_flags |= __fmtfl;
return __old;
}
/**
* @brief Setting new format flags.
* @param fmtfl Additional flags to set.
* @param mask The flags mask for @a fmtfl.
* @return The previous format control flags.
*
* This function clears @a mask in the format flags, then sets
* @a fmtfl @c & @a mask. An example mask is @c ios_base::adjustfield.
*/
fmtflags
setf(fmtflags __fmtfl, fmtflags __mask)
{
fmtflags __old = _M_flags;
_M_flags &= ~__mask;
_M_flags |= (__fmtfl & __mask);
return __old;
}
/**
* @brief Clearing format flags.
* @param mask The flags to unset.
*
* This function clears @a mask in the format flags.
*/
void
unsetf(fmtflags __mask)
{ _M_flags &= ~__mask; }
/**
* @brief Flags access.
* @return The precision to generate on certain output operations.
*
* Be careful if you try to give a definition of "precision" here; see
* DR 189.
*/
streamsize
precision() const
{ return _M_precision; }
/**
* @brief Changing flags.
* @param prec The new precision value.
* @return The previous value of precision().
*/
streamsize
precision(streamsize __prec)
{
streamsize __old = _M_precision;
_M_precision = __prec;
return __old;
}
/**
* @brief Flags access.
* @return The minimum field width to generate on output operations.
*
* "Minimum field width" refers to the number of characters.
*/
streamsize
width() const
{ return _M_width; }
/**
* @brief Changing flags.
* @param wide The new width value.
* @return The previous value of width().
*/
streamsize
width(streamsize __wide)
{
streamsize __old = _M_width;
_M_width = __wide;
return __old;
}
// [27.4.2.4] ios_base static members
/**
* @brief Interaction with the standard C I/O objects.
* @param sync Whether to synchronize or not.
* @return True if the standard streams were previously synchronized.
*
* The synchronization referred to is @e only that between the standard
* C facilities (e.g., stdout) and the standard C++ objects (e.g.,
* cout). User-declared streams are unaffected. See
* http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch28s02.html
*/
static bool
sync_with_stdio(bool __sync = true);
// [27.4.2.3] ios_base locale functions
/**
* @brief Setting a new locale.
* @param loc The new locale.
* @return The previous locale.
*
* Sets the new locale for this stream, and then invokes each callback
* with imbue_event.
*/
locale
imbue(const locale& __loc);
/**
* @brief Locale access
* @return A copy of the current locale.
*
* If @c imbue(loc) has previously been called, then this function
* returns @c loc. Otherwise, it returns a copy of @c std::locale(),
* the global C++ locale.
*/
locale
getloc() const
{ return _M_ios_locale; }
/**
* @brief Locale access
* @return A reference to the current locale.
*
* Like getloc above, but returns a reference instead of
* generating a copy.
*/
const locale&
_M_getloc() const
{ return _M_ios_locale; }
// [27.4.2.5] ios_base storage functions
/**
* @brief Access to unique indices.
* @return An integer different from all previous calls.
*
* This function returns a unique integer every time it is called. It
* can be used for any purpose, but is primarily intended to be a unique
* index for the iword and pword functions. The expectation is that an
* application calls xalloc in order to obtain an index in the iword and
* pword arrays that can be used without fear of conflict.
*
* The implementation maintains a static variable that is incremented and
* returned on each invocation. xalloc is guaranteed to return an index
* that is safe to use in the iword and pword arrays.
*/
static int
xalloc() throw();
/**
* @brief Access to integer array.
* @param __ix Index into the array.
* @return A reference to an integer associated with the index.
*
* The iword function provides access to an array of integers that can be
* used for any purpose. The array grows as required to hold the
* supplied index. All integers in the array are initialized to 0.
*
* The implementation reserves several indices. You should use xalloc to
* obtain an index that is safe to use. Also note that since the array
* can grow dynamically, it is not safe to hold onto the reference.
*/
long&
iword(int __ix)
{
_Words& __word = (__ix < _M_word_size)
? _M_word[__ix] : _M_grow_words(__ix, true);
return __word._M_iword;
}
/**
* @brief Access to void pointer array.
* @param __ix Index into the array.
* @return A reference to a void* associated with the index.
*
* The pword function provides access to an array of pointers that can be
* used for any purpose. The array grows as required to hold the
* supplied index. All pointers in the array are initialized to 0.
*
* The implementation reserves several indices. You should use xalloc to
* obtain an index that is safe to use. Also note that since the array
* can grow dynamically, it is not safe to hold onto the reference.
*/
void*&
pword(int __ix)
{
_Words& __word = (__ix < _M_word_size)
? _M_word[__ix] : _M_grow_words(__ix, false);
return __word._M_pword;
}
// Destructor
/**
* Invokes each callback with erase_event. Destroys local storage.
*
* Note that the ios_base object for the standard streams never gets
* destroyed. As a result, any callbacks registered with the standard
* streams will not get invoked with erase_event (unless copyfmt is
* used).
*/
virtual ~ios_base();
protected:
ios_base();
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 50. Copy constructor and assignment operator of ios_base
private:
ios_base(const ios_base&);
ios_base&
operator=(const ios_base&);
};
// [27.4.5.1] fmtflags manipulators
/// Calls base.setf(ios_base::boolalpha).
inline ios_base&
boolalpha(ios_base& __base)
{
__base.setf(ios_base::boolalpha);
return __base;
}
/// Calls base.unsetf(ios_base::boolalpha).
inline ios_base&
noboolalpha(ios_base& __base)
{
__base.unsetf(ios_base::boolalpha);
return __base;
}
/// Calls base.setf(ios_base::showbase).
inline ios_base&
showbase(ios_base& __base)
{
__base.setf(ios_base::showbase);
return __base;
}
/// Calls base.unsetf(ios_base::showbase).
inline ios_base&
noshowbase(ios_base& __base)
{
__base.unsetf(ios_base::showbase);
return __base;
}
/// Calls base.setf(ios_base::showpoint).
inline ios_base&
showpoint(ios_base& __base)
{
__base.setf(ios_base::showpoint);
return __base;
}
/// Calls base.unsetf(ios_base::showpoint).
inline ios_base&
noshowpoint(ios_base& __base)
{
__base.unsetf(ios_base::showpoint);
return __base;
}
/// Calls base.setf(ios_base::showpos).
inline ios_base&
showpos(ios_base& __base)
{
__base.setf(ios_base::showpos);
return __base;
}
/// Calls base.unsetf(ios_base::showpos).
inline ios_base&
noshowpos(ios_base& __base)
{
__base.unsetf(ios_base::showpos);
return __base;
}
/// Calls base.setf(ios_base::skipws).
inline ios_base&
skipws(ios_base& __base)
{
__base.setf(ios_base::skipws);
return __base;
}
/// Calls base.unsetf(ios_base::skipws).
inline ios_base&
noskipws(ios_base& __base)
{
__base.unsetf(ios_base::skipws);
return __base;
}
/// Calls base.setf(ios_base::uppercase).
inline ios_base&
uppercase(ios_base& __base)
{
__base.setf(ios_base::uppercase);
return __base;
}
/// Calls base.unsetf(ios_base::uppercase).
inline ios_base&
nouppercase(ios_base& __base)
{
__base.unsetf(ios_base::uppercase);
return __base;
}
/// Calls base.setf(ios_base::unitbuf).
inline ios_base&
unitbuf(ios_base& __base)
{
__base.setf(ios_base::unitbuf);
return __base;
}
/// Calls base.unsetf(ios_base::unitbuf).
inline ios_base&
nounitbuf(ios_base& __base)
{
__base.unsetf(ios_base::unitbuf);
return __base;
}
// [27.4.5.2] adjustfield manipulators
/// Calls base.setf(ios_base::internal, ios_base::adjustfield).
inline ios_base&
internal(ios_base& __base)
{
__base.setf(ios_base::internal, ios_base::adjustfield);
return __base;
}
/// Calls base.setf(ios_base::left, ios_base::adjustfield).
inline ios_base&
left(ios_base& __base)
{
__base.setf(ios_base::left, ios_base::adjustfield);
return __base;
}
/// Calls base.setf(ios_base::right, ios_base::adjustfield).
inline ios_base&
right(ios_base& __base)
{
__base.setf(ios_base::right, ios_base::adjustfield);
return __base;
}
// [27.4.5.3] basefield manipulators
/// Calls base.setf(ios_base::dec, ios_base::basefield).
inline ios_base&
dec(ios_base& __base)
{
__base.setf(ios_base::dec, ios_base::basefield);
return __base;
}
/// Calls base.setf(ios_base::hex, ios_base::basefield).
inline ios_base&
hex(ios_base& __base)
{
__base.setf(ios_base::hex, ios_base::basefield);
return __base;
}
/// Calls base.setf(ios_base::oct, ios_base::basefield).
inline ios_base&
oct(ios_base& __base)
{
__base.setf(ios_base::oct, ios_base::basefield);
return __base;
}
// [27.4.5.4] floatfield manipulators
/// Calls base.setf(ios_base::fixed, ios_base::floatfield).
inline ios_base&
fixed(ios_base& __base)
{
__base.setf(ios_base::fixed, ios_base::floatfield);
return __base;
}
/// Calls base.setf(ios_base::scientific, ios_base::floatfield).
inline ios_base&
scientific(ios_base& __base)
{
__base.setf(ios_base::scientific, ios_base::floatfield);
return __base;
}
iomanip:
/**
* @brief Manipulator for @c setf.
* @param mask A format flags mask.
*
* Sent to a stream object, this manipulator sets the format flags
* to @a mask.
*/
inline _Setiosflags
setiosflags(ios_base::fmtflags __mask)
{
_Setiosflags __x;
__x._M_mask = __mask;
return __x;
}
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setiosflags __f)
{
__is.setf(__f._M_mask);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setiosflags __f)
{
__os.setf(__f._M_mask);
return __os;
}
struct _Setbase { int _M_base; };
/**
* @brief Manipulator for @c setf.
* @param base A numeric base.
*
* Sent to a stream object, this manipulator changes the
* @c ios_base::basefield flags to @c oct, @c dec, or @c hex when @a base
* is 8, 10, or 16, accordingly, and to 0 if @a base is any other value.
*/
inline _Setbase
setbase(int __base)
{
_Setbase __x;
__x._M_base = __base;
return __x;
}
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setbase __f)
{
__is.setf(__f._M_base == 8 ? ios_base::oct :
__f._M_base == 10 ? ios_base::dec :
__f._M_base == 16 ? ios_base::hex :
ios_base::fmtflags(0), ios_base::basefield);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setbase __f)
{
__os.setf(__f._M_base == 8 ? ios_base::oct :
__f._M_base == 10 ? ios_base::dec :
__f._M_base == 16 ? ios_base::hex :
ios_base::fmtflags(0), ios_base::basefield);
return __os;
}
template<typename _CharT>
struct _Setfill { _CharT _M_c; };
/**
* @brief Manipulator for @c fill.
* @param c The new fill character.
*
* Sent to a stream object, this manipulator calls @c fill(c) for that
* object.
*/
template<typename _CharT>
inline _Setfill<_CharT>
setfill(_CharT __c)
{
_Setfill<_CharT> __x;
__x._M_c = __c;
return __x;
}
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setfill<_CharT> __f)
{
__is.fill(__f._M_c);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setfill<_CharT> __f)
{
__os.fill(__f._M_c);
return __os;
}
struct _Setprecision { int _M_n; };
/**
* @brief Manipulator for @c precision.
* @param n The new precision.
*
* Sent to a stream object, this manipulator calls @c precision(n) for
* that object.
*/
inline _Setprecision
setprecision(int __n)
{
_Setprecision __x;
__x._M_n = __n;
return __x;
}
template<typename _CharT, typename _Traits>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is, _Setprecision __f)
{
__is.precision(__f._M_n);
return __is;
}
template<typename _CharT, typename _Traits>
inline basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, _Setprecision __f)
{
__os.precision(__f._M_n);
return __os;
}
struct _Setw { int _M_n; };
/**
* @brief Manipulator for @c width.
* @param n The new width.
*
* Sent to a stream object, this manipulator calls @c width(n) for
* that object.
*/
inline _Setw
setw(int __n)
{
_Setw __x;
__x._M_n = __n;
return __x;
}
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