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Difference between revisions of "cpp/io/manip/showbase"

From cppreference.com
< cpp‎ | io‎ | manip
(z)
 
m (fmt, @@, capitalized 1st letter, {{c}}, ., headers sorted, langlinks)
 
(11 intermediate revisions by 3 users not shown)
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−
template<
+
{{cpp/title|showbase|noshowbase}}
−
    class charT,
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{{cpp/io/manip/navbar}}
−
    class Traits = std::char_traits<CharT>,  
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{{dcl begin}}
−
    class Allocator = std::allocator<CharT>  
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{{dcl header|ios}}
−
> class basic_filebuf;         //inherits basic_streambuf<charT, Traits, Allocator>
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{{dcl|num=1|
 +
std::ios_base& showbase( std::ios_base& str );
 +
}}
 +
{{dcl|num=2|
 +
std::ios_base& noshowbase( std::ios_base& str );
 +
}}
 +
{{dcl end}}
 +
 
 +
@1@ Enables the {{tt|showbase}} flag in the stream {{c|str}} as if by calling {{c|str.setf(std::ios_base::showbase)}}.
 +
 
 +
@2@ Disables the {{tt|showbase}} flag in the stream {{c|str}} as if by calling {{c|str.unsetf(std::ios_base::showbase)}}.
 +
 
 +
This is an I/O manipulator, it may be called with an expression such as {{c|out << std::showbase}} for any {{tt|out}} of type {{lc|std::basic_ostream}} or with an expression such as {{c|in >> std::showbase}} for any {{tt|in}} of type {{lc|std::basic_istream}}.
 +
 
 +
The {{tt|showbase}} flag affects the behavior of integer output (see {{lc|std::num_put::put}}), monetary input (see {{lc|std::money_get::get}}) and monetary output (see {{lc|std::money_put::put}}).
 +
 
 +
===Parameters===
 +
{{par begin}}
 +
{{par|str|reference to I/O stream}}
 +
{{par end}}
 +
 
 +
===Return value===
 +
{{c|str}} (reference to the stream after manipulation).
 +
 
 +
===Notes===
 +
As specifed in {{lc|std::num_put::put}}, the showbase flag in integer output acts like the # format specifier in {{lc|std::printf}}, which means the numeric base prefix is ''not'' added when outputting the value zero.
 +
 
 +
===Example===
 +
{{example
 +
|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===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/io/manip/dsc resetiosflags}}
 +
{{dsc inc|cpp/io/manip/dsc setiosflags}}
 +
{{dsc end}}
 +
 
 +
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 23:12, 15 September 2023

 
C++
 
Input/output library
 
Input/output manipulators
Floating-point formatting
Integer formatting
showbasenoshowbase
Boolean formatting
Field width and fill control
Other formatting
Whitespace processing
Output flushing
(C++20)  

Status flags manipulation
Time and money I/O
(C++11)
(C++11)
(C++11)
(C++11)
Quoted manipulator
(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).

Contents

[edit] Parameters

str - reference to I/O stream

[edit] Return value

str (reference to the stream after manipulation).

[edit] 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.

[edit] 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

[edit] See also

 clears the specified ios_base flags
(function) [edit]
sets the specified ios_base flags
(function) [edit]
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