C++ 출력 포맷

C++은 출력포맷을 맞춰주기 위해 다양한 포맷 입출력 기능을 제공한다.

ios 클래스에 포맷 플래그가 정의되어 있다.
https://msdn.microsoft.com/ko-kr/library/5yc0df6d.aspx 

Manipulators(조작자)는 다음과 같으며, 예를 들어 ios:fixed 와 같은 형태로 사용된다.

boolalpha	Specifies that variables of type bool appear as true or false in the stream.
dec	Specifies that integer variables appear in base 10 notation.
defaultfloat	Configures the flags of an ios_base object to use a default display format for float values.
fixed	Specifies that a floating-point number is displayed in fixed-decimal notation.
hex	Specifies that integer variables appear in base 16 notation.
internal	Causes a number's sign to be left justified and the number to be right justified.
left	Causes text that is not as wide as the output width to appear in the stream flush with the left margin.
noboolalpha	Specifies that variables of type bool appear as 1 or 0 in the stream.
noshowbase	Turns off indicating the notational base in which a number is displayed.
noshowpoint	Displays only the whole-number part of floating-point numbers whose fractional part is zero.
noshowpos	Causes positive numbers to not be explicitly signed.
noskipws	Cause spaces to be read by the input stream.
nounitbuf	Causes output to be buffered and processed when the buffer is full.
nouppercase	Specifies that hexadecimal digits and the exponent in scientific notation appear in lowercase.
oct	Specifies that integer variables appear in base 8 notation.
right	Causes text that is not as wide as the output width to appear in the stream flush with the right margin.
scientific	Causes floating point numbers to be displayed using scientific notation.
showbase	Indicates the notational base in which a number is displayed.
showpoint	Displays the whole-number part of a floating-point number and digits to the right of the decimal point even when the fractional part is zero.
showpos	Causes positive numbers to be explicitly signed.
skipws	Cause spaces to not be read by the input stream.
unitbuf	Causes output to be processed when the buffer is not empty.
uppercase	Specifies that hexadecimal digits and the exponent in scientific notation appear in uppercase.

또한 <iomanip>에는 << 와 >> 연산자와 함께 사용되는 조작자(manipulator)를 제공하는데, https://msdn.microsoft.com/ko-kr/library/ydd54a6t.aspx 다음과 같이 사용된다.

get_money	Obtains a monetary amount, optionally in international format.
get_time	Obtains a time in a time structure by using a specified format.
put_money	Provides a monetary amount, optionally in international format.
put_time	Provides a time in a time structure and a format string to use.
quoted	Enables convenient round-tripping of strings with insertion and extraction operators.
resetiosflags	Clears the specified flags.
setbase	Set base for integers.
setfill	Sets the character that will be used to fill spaces in a right-justified display.
setiosflags	Sets the specified flags.
setprecision	Sets the precision for floating-point values.
setw	Specifies the width of the display field.

 예를 들어 double value 값을 소수점 아래 둘째자리까지 출력하는데, 폭을 5로 맞춘다면

cout.setf(ios::fixed);
cout << "p = " <<  setw(5) << setprecision(2) << value<< endl; 

또는

  // <iomanip> 사용
  cout << fixed << setprecision(3) << "x = " << x << ", y = " << y << endl;

와 같이 사용한다.