NAME¶

std::num_put::put,std::num_put::do_put - std::num_put::put,std::num_put::do_put

Synopsis¶

Defined in header <locale>
public:

iter_type put( iter_type out, std::ios_base&
str,

char_type fill, bool val ) const;
iter_type put( iter_type out, std::ios_base&
str,
char_type fill, long val ) const;
iter_type put( iter_type out, std::ios_base&
str, (since C++11)
char_type fill, long long val )
const;
iter_type put( iter_type out, std::ios_base&
str,
char_type fill, unsigned long val
) const;
iter_type put( iter_type out, std::ios_base&
str, (since C++11)
char_type fill, unsigned long
long val ) const;
iter_type put( iter_type out, std::ios_base&
str,
char_type fill, double val )
const;
iter_type put( iter_type out, std::ios_base&
str,
char_type fill, long double val )
const;
iter_type put( iter_type out, std::ios_base&
str,
char_type fill, const void* val )
const;
protected: (1)

virtual iter_type do_put( iter_type out,
std::ios_base& str,

char_type fill, bool
val ) const;
virtual iter_type do_put( iter_type out,
std::ios_base& str,
char_type fill, long
val ) const;
virtual iter_type do_put( iter_type out,
std::ios_base& str, (since C++11)
char_type fill, long
long val ) const;
virtual iter_type do_put( iter_type out,
std::ios_base& str,
char_type fill, (2)
unsigned long val ) const;
virtual iter_type do_put( iter_type out,
std::ios_base& str, (since C++11)
char_type fill,
unsigned long long val ) const;
virtual iter_type do_put( iter_type out,
std::ios_base& str,
char_type fill, double
val ) const;
virtual iter_type do_put( iter_type out,
std::ios_base& str,
char_type fill, long
double val ) const;
virtual iter_type do_put( iter_type out,
std::ios_base& str,
char_type fill, const
void* val ) const;

1) Public member function, calls the protected virtual member function do_put of the
most derived class.
2) Writes characters to the output sequence out which represent the value of val,
formatted as requested by the formatting flags str.flags() and the std::numpunct and
std::ctype facets of the locale imbued in the stream str. This function is called by
all formatted output stream operators, such as std::cout << n;.

Conversion occurs in four stages:

Stage 1: conversion specifier selection¶

* I/O format flags are obtained, as if by

fmtflags basefield = (str.flags() & std::ios_base::basefield);
fmtflags uppercase = (str.flags() & std::ios_base::uppercase);
fmtflags floatfield = (str.flags() & std::ios_base::floatfield);
fmtflags showpos = (str.flags() & std::ios_base::showpos);
fmtflags showbase = (str.flags() & std::ios_base::showbase);
fmtflags showpoint = (str.flags() & std::ios_base::showpoint);
* If the type of val is bool:
* If boolalpha == 0, then converts val to type int and performs integer
output.
* If boolalpha != 0, obtains
std::use_facet<std::numpunct<CharT>>(str.getloc()).truename() if val ==
true or std::use_facet<std::numpunct<CharT>>(str.getloc()).falsename() if
val == false, and outputs each successive character c of that string to out
with *out++ = c. No further processing is done in this case, the function
returns out.
* If the type of val is an integer type, the first applicable choice of the
following is selected:
* If basefield == oct, will use conversion specifier %o
* If basefield == hex && !uppercase, will use conversion specifier %x
* If basefield == hex, will use conversion specifier %X
* If the type of val is signed, will use conversion specifier %d
* If the type of val is unsigned, will use conversion specifier %u
* For integer types, length modifier is added to the conversion specification if
necessary: l for long and unsigned long
, ll for long long and unsigned long long
(since C++11).
* If the type of val is a floating-point type, the first applicable choice of the
following is selected:
* If floatfield == std::ios_base::fixed, will use conversion specifier %f
* If floatfield == std::ios_base::scientific && !uppercase, will use
conversion specifier %e
* If floatfield == std::ios_base::scientific, will use conversion specifier
%E

* If floatfield == (std::ios_base::fixed |
std::ios_base::scientific) && !uppercase, will use conversion
specifier %a (since C++11)
* If floatfield == (std::ios_base::fixed |
std::ios_base::scientific), will use conversion specifier %A

* If !uppercase, will use conversion specifier %g
* Otherwise, will use conversion specifier %G
Also:
* If the type of val is long double, the length modifier L is added to the
conversion specifier.
* If the type of val is a floating-point type
and floatfield != (ios_base::fixed | ios_base::scientific)
(since C++11), the precision modifier is added and set to str.precision().
Otherwise, no precision is specified.
* For both integer and floating-point types, if showpos is set, the modifier + is
prepended
* For integer types, if showbase is set, the modifier # is prepended.
* For floating-point types, if showpoint is set, the modifier # is prepended.
* If the type of val is void*, will use conversion specifier %p
* A narrow character string is created as if by a call to std::printf(spec, val)
in the "C" locale, where spec is the chosen conversion specifier.

Stage 2: locale-specific conversion¶

* Every character c obtained in Stage 1, other than the decimal point '.', is
converted to CharT by calling
std::use_facet<std::ctype<CharT>>(str.getloc()).widen(c).
* For arithmetic types, the thousands separator character, obtained from
std::use_facet<std::numpunct<CharT>>(str.getloc()).thousands_sep(), is inserted
into the sequence according to the grouping rules provided by
std::use_facet<std::numpunct<CharT>>(str.getloc()).grouping()
* Decimal point characters ('.') are replaced by
std::use_facet<std::numpunct<CharT>>(str.getloc()).decimal_point()

Stage 3: padding¶

* The adjustment flag is obtained as if by std::fmtflags adjustfield = (flags &
(std::ios_base::adjustfield)) and examined to identify padding location, as
follows:
* If adjustfield == std::ios_base::left, will pad after
* If adjustfield == std::ios_base::right, will pad before
* If adjustfield == std::ios_base::internal and a sign character occurs in
the representation, will pad after the sign
* If adjustfield == std::ios_base::internal and Stage 1 representation began
with 0x or 0X, will pad after the x or X
* Otherwise, will pad before
* If str.width() is non-zero (e.g. std::setw was just used) and the number of
CharT's after Stage 2 is less than str.width(), then copies of the fill
character are inserted at the position indicated by padding to bring the length
of the sequence to str.width().

In any case, str.width(0) is called to cancel the effects of std::setw.

Stage 4: output¶

Every successive character c from the sequence of CharT's from Stage 3 is output as
if by *out++ = c.

Parameters¶

out - iterator pointing to the first character to be overwritten
str - stream to retrieve the formatting information from
fill - padding character used when the results needs to be padded to the field width
val - value to convert to string and output

Return value¶

out

Notes¶

The leading zero generated by the conversion specification #o (resulting from the
combination of std::showbase and std::oct for example) is not counted as a padding
character.

When formatting a floating point value as hexfloat (i.e., when
floatfield == (std::ios_base::fixed | std::ios_base::scientific)), the (since C++11)
stream's precision is not used; instead, the number is always printed
with enough precision to exactly represent the value.

Example¶

Output a number using the facet directly, and demonstrate user-defined facet:

// Run this code

#include <iostream>
#include <locale>

// this custom num_put outputs squares of all integers (except long long)
struct squaring_num_put : std::num_put<char>
{
iter_type do_put(iter_type out, std::ios_base& str,
char_type fill, long val) const
{
return std::num_put<char>::do_put(out, str, fill, val * val);
}

iter_type do_put(iter_type out, std::ios_base& str,
char_type fill, unsigned long val) const
{
return std::num_put<char>::do_put(out, str, fill, val * val);
}
};

int main()
{
auto& facet = std::use_facet<std::num_put<char>>(std::locale());
facet.put(std::cout, std::cout, '0', 2.71);
std::cout << '\n';

std::cout.imbue(std::locale(std::cout.getloc(), new squaring_num_put));
std::cout << 6 << ' ' << -12 << '\n';
}

Output:¶

2.71
36 144

An implementation of operator<< for a user-defined type.

// Run this code

#include <iostream>
#include <iterator>
#include <locale>

struct base { long x = 10; };

template<class CharT, class Traits>
std::basic_ostream<CharT, Traits>&
operator<<(std::basic_ostream<CharT, Traits>& os, base const& b)
{
try
{
typename std::basic_ostream<CharT, Traits>::sentry s(os);

if (s)
{
std::ostreambuf_iterator<CharT, Traits> it(os);
std::use_facet<std::num_put<CharT>>(os.getloc())
.put(it, os, os.fill(), b.x);
}
}
catch (...)
{
// set badbit on os and rethrow if required
}

return os;
}

int main()
{
base b;
std::cout << b;
}

Output:¶

10

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
the bool overload used non-existing use these members of
LWG 34 C++98 members std::numpunct
truename and falsename of std::ctype
the precision modifier was only added
LWG 231 C++98 if removed these conditions
(flags & fixed) != 0 or str.precision()
> 0
LWG 282 C++98 the thousand separators were only also inserted for
inserted for integral types in stage 2 floating-point types

See also¶

operator<< inserts formatted data
(public member function of std::basic_ostream<CharT,Traits>)