public member function
<ios> <iostream>
| set (1) | fmtflags setf (fmtflags fmtfl); |
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| mask (2) | fmtflags setf (fmtflags fmtfl, fmtflags mask); |
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Set specific format flags
The first form (1) sets the stream's format flags whose bits are set in fmtfl, leaving unchanged the rest, as if a call to flags(fmtfl|flags()).
The second form (2) sets the stream's format flags whose bits are set in both fmtfl and mask, and clears the format flags whose bits are set in mask but not in fmtfl, as if a call to flags((fmtfl&mask)|(flags()&~mask)).
Both return the value of the stream's format flags before the call.
The format flags of a stream affect the way data is interpreted in certain input functions and how it is written by certain output functions. See ios_base::fmtflags for the possible values of this function's arguments.
The first form of setf (1) is generally used to set independent format flags: boolalpha, showbase, showpoint, showpos, skipws, unitbuf and uppercase, which can also be unset directly with member unsetf.
The second form (2) is generally used to set a value for one of the selective flags, using one of the field bitmasks as the mask argument:
fmtfl
format flag value | mask
field bitmask |
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| left, right or internal | adjustfield |
| dec, oct or hex | basefield |
| scientific or fixed | floatfield |
The parameterized manipulator setiosflags behaves in a similar way as the first form of this member function (1).
Parameters
- fmtfl
- Format flags to be set. If the second syntax is used, only the bits set in both fmtfl and mask are set in the stream's format flags; the flags set in mask but not in fmtfl are cleared.
- mask
- Mask containing the flags to be modified.
Member type fmtflags is a bitmask type (see ios_base::fmtflags).
Return Value
The format flags selected in the stream before the call.
Example
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// modifying flags with setf/unsetf
#include <iostream> // std::cout, std::ios
int main () {
std::cout.setf ( std::ios::hex, std::ios::basefield ); // set hex as the basefield
std::cout.setf ( std::ios::showbase ); // activate showbase
std::cout << 100 << '\n';
std::cout.unsetf ( std::ios::showbase ); // deactivate showbase
std::cout << 100 << '\n';
return 0;
}
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Output:
Data races
Modifies the stream object.
Concurrent access to the same stream object may cause data races.
Exception safety
Basic guarantee: if an exception is thrown, the stream is in a valid state.