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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setfill setw	internalleftright
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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 <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 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)