std::showbase, std::noshowbase

 

C++

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Feature test macros (C++20)

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I/O manipulators

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C-style I/O

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basic_streambuf

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basic_ispanstream (C++23)

basic_ospanstream (C++23)

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Synchronized Output

basic_osyncstream (C++20)

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streamoff

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fpos

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iostream_category (C++11)

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Input/output manipulators

Floating-point formatting
showpointnoshowpoint setprecision	fixedscientifichexfloatdefaultfloat (C++11)(C++11)
Integer formatting
setbase showbasenoshowbase	dechexoct
Boolean formatting
boolalphanoboolalpha
Field width and fill control
setfill setw	internalleftright
Other formatting
showposnoshowpos	uppercasenouppercase
Whitespace processing
ws ends	skipwsnoskipws
Output flushing
flush endl flush_emit (C++20)	unitbufnounitbuf emit_on_flushnoemit_on_flush (C++20)(C++20)
Status flags manipulation
resetiosflags	setiosflags
Time and money I/O
get_money (C++11) get_time (C++11)	put_money (C++11) put_time (C++11)
Quoted manipulator
quoted (C++14)

 

Defined in header <ios>
std::ios_base& showbase( std::ios_base& str );	(1)
std::ios_base& noshowbase( std::ios_base& str );	(2)

1) Enables the showbase flag in the stream str as if by calling str.setf(std::ios_base::showbase).

2) Disables the showbase flag in the stream str as if by calling str.unsetf(std::ios_base::showbase).

This is an I/O manipulator, it may be called with an expression such as out << std::showbase for any out of type std::basic_ostream or with an expression such as in >> std::showbase for any in of type std::basic_istream.

The showbase flag affects the behavior of integer output (see std::num_put::put), monetary input (see std::money_get::get) and monetary output (see std::money_put::put).

Parameters

str

-

reference to I/O stream

Return value

str (reference to the stream after manipulation).

Notes

As specifed in std::num_put::put, the showbase flag in integer output acts like the # format specifier in std::printf, which means the numeric base prefix is not added when outputting the value zero.

Example

Run this code

#include <iomanip>
#include <iostream>
#include <locale>
#include <sstream>
 
int main()
{
    // showbase affects the output of octals and hexadecimals
    std::cout << std::hex
              << "showbase: " << std::showbase << 42 << '\n'
              << "noshowbase: " << std::noshowbase << 42 << '\n';
 
    // and both input and output of monetary values
    std::locale::global(std::locale("en_US.utf8"));
    long double val = 0;
    std::istringstream is("3.14");
    is >> std::showbase >> std::get_money(val);
    std::cout << "With showbase, parsing 3.14 as money gives " << val << '\n';
    is.seekg(0);
    is >> std::noshowbase >> std::get_money(val);
    std::cout << "Without showbase, parsing 3.14 as money gives " << val << '\n';
}

Output:

showbase: 0x2a
noshowbase: 2a
With showbase, parsing 3.14 as money gives 0
Without showbase, parsing 3.14 as money gives 314

See also

resetiosflags	clears the specified ios_base flags (function)
setiosflags	sets the specified ios_base flags (function)