The GNU C++ Iostream Library - Format Control

Choices in formatting

These methods control (or report on) settings for some details of controlling streams, primarily to do with formatting output:

Method char ios::fill () const

Report on the padding character in use.

Method char ios::fill (char padding)

Set the padding character. You can also use the manipulator setfill . See Changing stream properties in expressions.

Default: blank.

Method int ios::precision () const

Report the number of significant digits currently in use for output of floating point numbers.

Default: 6 .

Method int ios::precision (int signif)

Set the number of significant digits (for input and output numeric conversions) to signif.

You can also use the manipulator setprecision for this purpose. See Changing stream properties using manipulators.

Method int ios::width () const

Report the current output field width setting (the number of characters to write on the next `<<' output operation).

Default: 0 , which means to use as many characters as necessary.

Method int ios::width (int num)

Set the input field width setting to num. Return the previous value for this stream.

This value resets to zero (the default) every time you use `<<'; it is essentially an additional implicit argument to that operator. You can also use the manipulator setw for this purpose. See Changing stream properties using manipulators.

Method fmtflags ios::flags () const

Return the current value of the complete collection of flags controlling the format state. These are the flags and their meanings when set:

ios::dec

ios::oct

ios::hex

What numeric base to use in converting integers from internal to display representation, or vice versa: decimal, octal, or hexadecimal, respectively. (You can change the base using the manipulator setbase , or any of the manipulators dec , oct , or hex ; see Changing stream properties in expressions.)

On input, if none of these flags is set, read numeric constants according to the prefix: decimal if no prefix (or a `.' suffix), octal if a `0' prefix is present, hexadecimal if a `0x' prefix is present.

Default: dec .

ios::fixed

Avoid scientific notation, and always show a fixed number of digits after the decimal point, according to the output precision in effect. Use ios::precision to set precision.

ios::left

ios::right

ios::internal

Where output is to appear in a fixed-width field; left-justified, right-justified, or with padding in the middle (e.g. between a numeric sign and the associated value), respectively.

ios::scientific

Use scientific (exponential) notation to display numbers.

ios::showbase

Display the conventional prefix as a visual indicator of the conversion base: no prefix for decimal, `0' for octal, `0x' for hexadecimal.

ios::showpoint

Display a decimal point and trailing zeros after it to fill out numeric fields, even when redundant.

ios::showpos

Display a positive sign on display of positive numbers.

ios::skipws

Skip white space. (On by default).

ios::stdio

Flush the C stdio streams stdout and stderr after each output operation (for programs that mix C and C++ output conventions).

ios::unitbuf

Flush after each output operation.

ios::uppercase

Use upper-case characters for the non-numeral elements in numeric displays; for instance, `0X7A' rather than `0x7a', or `3.14E+09' rather than `3.14e+09'.

Method fmtflags ios::flags (fmtflags value)

Set value as the complete collection of flags controlling the format state. The flag values are described under `ios::flags ()'.

Use ios::setf or ios::unsetf to change one property at a time.

Method fmtflags ios::setf (fmtflags flag)

Set one particular flag (of those described for `ios::flags ()'; return the complete collection of flags previously in effect. (Use ios::unsetf to cancel.)

Method fmtflags ios::setf (fmtflags flag, fmtflags mask)

Clear the flag values indicated by mask, then set any of them that are also in flag. (Flag values are described for `ios::flags ()'.) Return the complete collection of flags previously in effect. (See ios::unsetf for another way of clearing flags.)

Method fmtflags ios::unsetf (fmtflags flag)

Make certain flag (a combination of flag values described for `ios::flags ()') is not set for this stream; converse of ios::setf . Returns the old values of those flags.