std::setbase

 

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showpointnoshowpoint setprecision	fixedscientifichexfloatdefaultfloat (C++11)(C++11)
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setbase showbasenoshowbase	dechexoct
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boolalphanoboolalpha
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showposnoshowpos	uppercasenouppercase
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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 <iostream>
#include <sstream>
#include <iomanip>
 
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 of type std::ostream or std::istream	usable with any character stream

See also

dechexoct	changes the base used for integer I/O (function)
showbasenoshowbase	controls whether prefix is used to indicate numeric base (function)