C++ ios_base fmtflags

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Description

This type is used as its parameter and/or return value by the member functions flags, setf and unsetf.

Declaration

Following is the declaration for ios_base::fmtflags.

std::ios_base::fmtflags ff;

The values passed and retrieved by these functions can be any valid combination of the following member constants as shown below −

field	member constant	effect when set
independent flags	boolalpha	read/write bool elements as alphabetic strings (true and false).
	showbase	write integral values preceded by their corresponding numeric base prefix.
	showpoint	write floating-point values including always the decimal point.
	showpos	write non-negative numerical values preceded by a plus sign (+).
	skipws	skip leading whitespaces on certain input operations.
	unitbuf	flush output after each inserting operation.
	uppercase	write uppercase letters replacing lowercase letters in certain insertion operations.
numerical base (basefield)	dec	read/write integral values using decimal base format.
	hex	read/write integral values using hexadecimal base format.
	oct	read/write integral values using octal base format.
float format (floatfield)	fixed	write floating point values in fixed-point notation.
	scientific	write floating-point values in scientific notation.
adjustment (adjustfield)	internal	the output is padded to the field width by inserting fill characters at a specified internal point.
	left	the output is padded to the field width appending fill characters at the end.
	right	the output is padded to the field width by inserting fill characters at the beginning.

Three additional bitmask constants made of the combination of the values of each of the three groups of selective flags can also be used as shown below.

flag value	equivalent to
adjustfield	left | right | internal
basefield	dec | oct | hex
floatfield	scientific | fixed

The values of these constants can be combined into a single fmtflags value using the OR bitwise operator (|).

Example

In below example is shown for ios_base::fmtflags.

#include <iostream>

int main () {

   std::cout.setf (std::ios_base::hex , std::ios_base::basefield);
   std::cout.setf (std::ios_base::showbase);
   std::cout << 100 << '\n';

   std::cout.setf (std::ios::hex , std::ios::basefield);
   std::cout.setf (std::ios::showbase);
   std::cout << 100 << '\n';

   std::cout.setf (std::cout.hex , std::cout.basefield);
   std::cout.setf (std::cout.showbase);
   std::cout << 100 << '\n';

   std::ios_base::fmtflags ff;
   ff = std::cout.flags();
   ff &= ~std::cout.basefield;   
   ff |= std::cout.hex;          
   ff |= std::cout.showbase;     
   std::cout.flags(ff);
   std::cout << 100 << '\n';

   std::cout << std::hex << std::showbase << 100 << '\n';

   return 0;
}

Let us compile and run the above program, this will produce the following result −

0x64
0x64
0x64
0x64
0x64