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Optional_character
flags You can use the following flag characters, alone or in
any combined order, to modify the conversion
specification:
' Requests that a numeric conversion is
formatted with the thousands separator
character. Only the numbers to the left of
the radix character are formatted with the
separator character. The character used as
a separator and the positioning of the
separators are defined in the program's
current locale.
-(hyphen) Left-justifies the converted output source
in its field.
+ Requests that an explicit sign be present on
a signed conversion. If this flag is not
specified, the result of a signed conversion
begins with a sign only when a negative
value is converted.
space Prefixes a space to the result of a signed
conversion, if the first character of the
conversion is not a sign, or if the
conversion results in no characters. If you
specify both the space and the + flag, the
space flag is ignored.
# Requests an alternate form conversion.
Depending on the conversion specified,
different actions will occur. For the o
(octal) conversion, the precision is
increased to force the first digit to be a
0. For the x (or X) conversion, a nonzero
result is prefixed with 0x (or 0X). For e,
E, f, g, and G conversions, the result
contains a decimal point even at the end of
an integer value. For g and G conversions,
trailing zeros are not trimmed. For other
conversions, the effect of # is undefined.
0 Uses zeros rather than spaces to pad the
field width for d, i, o, u, x, X, e, E, f,
g, and G conversions. If both the 0 and the
- flags are specified, then the 0 flag is
ignored. For d, i, o, u, x, and X
conversions, if a precision is specified,
the 0 flag is ignored. For other
conversions, the behavior of the 0 flag is
undefined.
field width The minimum field width can be designated by a decimal
integer constant, or by an output source. To specify
an output source, use an asterisk (*) or the sequence
*n$, where n refers to the nth output source listed
after the format specification. If the converted
output source is wider than the minimum field, write
it out. If the converted output source is narrower
than the minimum width, pad it to make up the field
width. Pad with spaces, by default. Pad with zeros
if the 0 flag is specified; this does not mean that
the width is an octal number. Padding is on the left
by default, and on the right if a minus sign is
specified.
period (.) Separates the field width from the precision.
precision The precision defines the minimum number of digits to
appear for d, i, o, u, x, and X conversions; the
number of digits to appear after the decimal-point
character for e, E, and f conversions; the maximum
number of significant digits for g and G conversions;
or the maximum number of characters to be written from
a string in an s or S conversion. If a precision
appears with any other conversion specifier, the
behavior is undefined.
Precision can be designated by a decimal integer
constant, or by an output source. To specify an
output source, use an asterisk (*) or the sequence
*n$, where n refers to the nth output source listed
after the format specification.
If only the period is specified, the precision is
taken as 0.
h, l, or L An h specifies that a following d, i, o, u, x, or X
conversion specifier applies to a short int or
unsigned short int argument; an h can also specify
that a following n conversion specifier applies to a
pointer to a short int argument.
An l (lowercase ell) specifies that a following d, i,
o, u, x, or X conversion specifier applies to a long
int or unsigned long int argument; an l can also
specify that a following n conversion specifier
applies to a pointer to a long int argument.
An L specifies that a following e, E, f, g, or G
conversion specifier applies to a long double
argument.
If an h, l, or L appears with any other conversion
specifier, the behavior is undefined.
On Compaq C for OpenVMS VAX and Alpha Systems, int
values are equivalent to long values.
Conversion_Specifier
d, i Converts an int argument to signed decimal format.
o Converts an unsigned int argument to unsigned octal
format.
u Converts an unsigned int argument to unsigned decimal
format (giving a number in the range 0 to 4,294,967,295).
x, X Converts an unsigned int argument to unsigned hexadecimal
format (with or without a leading 0x). The letters
'abcdef' are used for the x conversion; the letters
'ABCDEF' are used for the X conversion.
f Converts a float or double argument to the format
[-]mmm.nnnnnn. The number of n's is equal to the
precision specification. If no precision is specified,
the default is 6.
If the precision is 0 and the # flag is specified, the
decimal point appears but no n's appear. If the precision
is 0 and the # flag is not specified, the decimal point
also does not appear. If a decimal point appears, at
least one digit appears before it. The value is rounded
to the appropriate number of digits.
e, E Converts a float or double argument to the format
[-]m.nnnnnnE[+|-]xx. The number of n's is specified by
the precision. If no precision is specified, the default
is 6. If the precision is explicitly 0 and the # flag is
specified, the decimal point appears but no n's appear.
If the precision is explicitly 0 and the # flag is not
specified, the decimal point also does not appear. An 'e'
is printed for e conversion; an 'E' is printed for E
conversion. The exponent always contains at least two
digits. If the value is 0, the exponent is 0.
g, G Converts a float or double argument to format f or e (or E
if the G conversion specifier is used), with the precision
specifying the number of significant digits. If the
precision is 0, it is taken as 1. The format used depends
on the value of the argument: format e (or E) is used
only if the exponent resulting from such a conversion is
less than -4, or is greater than or equal to the
precision; otherwise, format f is used. Trailing zeros
are suppressed in the fractional portion of the result. A
decimal point appears only if it is followed by a digit.
c Converts an int argument to an unsigned char, and writes
the resulting character (null characters are ignored).
C Converts a wchar_t argument to an array of bytes
representing the character, and writes the resulting
character. If the field width is specified and the
resulting character occupies fewer bytes than the field
width, it will be padded to the given width with space
characters. If the precision is specified, the behavior
is undefined.
s Requires an argument that is a pointer to an array of
characters of type char. The argument is used to write
characters until a null character is encountered or until
the number of characters indicated by the precision
specification is exhausted. If the precision
specification is 0 or omitted, all characters up to a null
are output.
S Converts an array of wide-character codes to multibyte
characters, and writes the multibyte characters. Requires
an argument that is a pointer to an array of wide
characters of type wchar_t. Characters are written until
a null wide character is encountered or until the number
of bytes indicated by the precision specification is
exhausted. If the precision specification is omitted or
is greater than the size of the array of converted bytes,
the array of wide characters must be terminated by a null
wide character.
p Requires an argument that is a pointer to void. The value
of the pointer is output as a hexadecimal character.
n Requires an argument that is a pointer to an integer. The
integer is assigned the number of characters written to
the output stream so far by this call to the formatted
output function. No argument is converted.
% Writes out the percent symbol. No conversion is
performed. The complete conversion specification would be
%%.
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