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The member function tt(setf()) is used to define the way numbers are
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displayed. It expects one or two arguments, all em(flags) of the tt(iostream)
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class. In the following examples, tt(cout) is used, but other tt(ostream)
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objects might have been used as well:
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it() To display the numeric base of integral values, use
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centt(cout.setf(ios::showbase))
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This results in em(no) prefix for decimal values, tt(0x) for hexadecimal
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values, tt(0) for octal values. For example:
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cout.setf(ios::showbase);
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cout << 16 << ", " << hex << 16 << ", " << oct << 16 << '\n';
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it() To display a trailing decimal point and trailing decimal zeros when
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real numbers are displayed, use
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centt(cout.setf(ios::showpoint))
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cout.setf(ios::showpoint);
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cout << 16.0 << ", " << 16.1 << ", " << 16 << '\n';
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centt(16.0000, 16.1000, 16)
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Note that the last tt(16) is an integral rather than a real number, and is not
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given a decimal point.
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If tt(ios::showpoint) is not used, then trailing zeros are discarded. If the
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decimal part is zero, then the decimal point is discarded as well.
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it() Comparable to the tt(dec, hex) and tt(oct) manipulators
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cout.setf(ios::dec, ios::basefield);
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cout.setf(ios::hex, ios::basefield);
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cout.setf(ios::oct, ios::basefield);
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it() To control the way real numbers are displayed tt(cout.setf(ios::fixed,
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ios::floatfield)) or tt(cout.setf(ios::scientific, ios::floatfield)) can be
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used. These settings result in, respectively, a fixed value display or a
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scientific (power of 10) display of numbers. For example,
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cout.setf(ios::fixed, ios::floatfield);
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cout << sqrt(200) << '\n';
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cout.setf(ios::scientific, ios::floatfield);
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cout << sqrt(200) << '\n';
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itt(ios::left): This format state is used to left-adjust the display
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of values for which the tt(setw()) manipulator (see below) is used. The format
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state can be set using the tt(setf()) member function, and it can be unset
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using the tt(unsetf()) member function. By default values are right-adjusted.
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itt(ios::internal): This format state will add the fill-characters
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(blanks by default) between the minus sign of negative numbers and the value
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With tt(istream) objects the flag tt(ios::skipws) can be used to control the
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handling of whitespace characters when characters are extracted. Leading white
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space characters of numerical values are skipped when
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tt(istreamObject.unsetf(ios::skipws)) has been specified, but otherwise they
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must be read explicitly. Reading a tt(char *) or tt(string) variable in this
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situation will only succeed if the first character to be read isn't a
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white-space character. The following small program can be used to illustrate
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the effects of unsetting tt(ios::skipws):
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cin.unsetf(ios::skipws);
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cin >> i; // skips leading ws
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cin >> buffer; // doesn't skip leading ws.
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cout << "got " << i << " and " << buffer << '\n';
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while (cin >> c) // reads individual chars, if the previous
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cout << "got '" << c << "'\n"; // extraction succeeded.
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itt(setf(ios::showbase)) is used to display the numeric base of integral
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itt(setf(ios::showpoint)) is used to display the trailing decimal point
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and trailing zeros of real numbers
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itt(setf(ios::dec, ios::basefield), setf(ios::hex, ios::basefield)) and
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tt(setf(ios::oct, ios::basefield)) can be used instead of the tt(dec, hex) and
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tt(oct) manipulators.
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itt(cout.setf(ios::scientific, ios::floatfield)) and
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tt(cout.setf(ios::fixed, ios::floatfield)) can be used to obtain a fixed or
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scientific (power of 10) display of real values.
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itt(setf(ios::left)) is used to left-adjust values in the width of
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itt(setf(ios::internal)) is used to left-adjust the minus sign of negative
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values (while the values themselves are right adjusted).
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itt(ios::skipws) is used to control the handling of white space characters
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by the extraction operator.
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To em(unset) flags, the function tt(unsetf()) can be used.
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yo/iostreams/src/setf.yo.OFF
