std::setbase(3)

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)