# std::setbase

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< cpp‎ | io‎ | manip

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

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

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