std::setbase
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setbase
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(C++14)
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
basefieldto 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.
[edit] Parameters
base
-
new value for basefield
[edit] 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 ); }
[edit] 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
[edit] 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 streamsof type std::ostream or std::istream |
usable with any character stream |