cout.setf() 与 cout.precision() C

大家都知道：cout.setf()是用来设置位的，cout.precision()是用来设置精度的，但具体如何操作想必难倒一批人！

std::ios_base::setf或者 std::ios::setf
C++ Input/output library std::ios_base


fmtflags setf( fmtflags flags );	(1)

fmtflags setf( fmtflags flags, fmtflags mask );	(2)

Sets the formatting flags to specified settings.
1) Sets the formatting flags to flags
2) Clears the formatting flags under mask, and sets the cleared flags to those specified by flags. Essentially the following operation is performed(flags & mask) where fl defines the state of internal formatting flags.
Parameters

flags, mask

new formatting setting. mask defines which flags can be altered, flags defines which flags of those to be altered should be set (others will be cleared). Both parameters can be a combination of the following constants:


Constant	Explanation

`dec`	use decimal base for integer I/O

`oct`	use octal base for integer I/O

`hex`	use hexadecimal base for integer I/O

`basefield`	dec\|oct\|hex\|0. Useful for masking operations由此向上四个是一组

`left`	left adjustment (adds fill characters to the right)

`right`	right adjustment (adds fill characters to the left)

`internal`	internal adjustment (adds fill characters to the internal designated point)

`adjustfield`	left\|right\|internal. Useful for masking operations由此向上四个是一组

`scientific`	generate floating point types using scientific notation, or hex notation if combined with fixed

`fixed`	generate floating point types using fixed notation, or hex notation if combined with scientific

`floatfield`	scientific\|fixed\|(scientific\|fixed)\|0. Useful for masking operations由此向上3个是一组

`boolalpha`	insert and extract bool type in alphanumeric format

`showbase`	generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O

`showpoint`	generate a decimal-point character unconditionally for floating-point number output

`showpos`	generate a + character for non-negative numeric output

`skipws`	skip leading whitespace before certain input operations

`unitbuf`	flush the output after each output operation

`uppercase`	replace certain lowercase letters with their uppercase equivalents in certain output output operations

【cout.setf() 与 cout.precision()】例子：

C/C++ code?

1 2 3 4 5 6 7 8 9 10 11 #include usingnamespacestd; intmain () { cout.setf ( ios::hex, ios::basefield ); // set hex as the basefield cout.setf ( ios::showbase ); // activate showbase cout << 100 << endl; cout.setf ( 0, ios::showbase ); // deactivate showbase cout << 100 << endl; return0; }

输出：
0x64
64

setprecision：
C/C++ code?

1 2 3 4 5 6 7 8 9 10 11 12 13 #include #include usingnamespacestd; intmain () { doublef =3.14159; cout << setprecision (5) << f << endl; cout << setprecision (9) << f << endl; cout << fixed; cout << setprecision (5) << f << endl; cout << setprecision (9) << f << endl; return0; }