NAME¶

std::setbase - std::setbase

Synopsis¶

Defined in header <iomanip>
/*unspecified*/ setbase( int base );

Sets the numeric base of the stream. When used in an expression out << setbase(base)
or in >> setbase(base), changes the basefield flag of the stream out or in,
depending on the value of base:

* the value 16 sets basefield to std::ios_base::hex.
* the value 8 sets std::ios_base::oct.
* the value 10 sets std::ios_base::dec.

Values of base other than 8, 10, or 16 reset basefield to zero, which corresponds to
decimal output and prefix-dependent input.

Parameters¶

base - new value for basefield

Return value¶

An object of unspecified type such that

* if out is an object of type std::basic_ostream<CharT, Traits>, the expression
out << setbase(base)
* has type std::basic_ostream<CharT, Traits>&
* has value out
* behaves as if it called f(out, base)
* if in is an object of type std::basic_istream<CharT, Traits>, the expression in
>> setbase(base)
* has type std::basic_istream<CharT, Traits>&
* has value in
* behaves as if it called f(in, base)

where the function f is defined as:

void f(std::ios_base& str, int base)
{
// set basefield
str.setf(base == 8 ? std::ios_base::oct :
base == 10 ? std::ios_base::dec :
base == 16 ? std::ios_base::hex :
std::ios_base::fmtflags(0), std::ios_base::basefield);
}

Example¶

// Run this code

#include <iomanip>
#include <iostream>
#include <sstream>

int main()
{
std::cout << "Parsing string \"10 0x10 010\"\n";

int n1, n2, n3;
std::istringstream s("10 0x10 010");

s >> std::setbase(16) >> n1 >> n2 >> n3;
std::cout << "hexadecimal parse: " << n1 << ' ' << n2 << ' ' << n3 << '\n';

s.clear();
s.seekg(0);

s >> std::setbase(0) >> n1 >> n2 >> n3;
std::cout << "prefix-dependent parse: " << n1 << ' ' << n2 << ' ' << n3 << '\n';

std::cout << "hex output: " << std::setbase(16)
<< std::showbase << n1 << ' ' << n2 << ' ' << n3 << '\n';
}

Output:¶

Parsing string "10 0x10 010"
hexadecimal parse: 16 16 16
prefix-dependent parse: 10 16 8
hex output: 0xa 0x10 0x8

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 183 C++98 setbase could only be used with streams usable with any
of type std::ostream or std::istream character stream

See also¶

dec changes the base used for integer I/O
hex (function)
oct
showbase controls whether prefix is used to indicate numeric base
noshowbase (function)