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Fprintf places output on the named output stream f (see fopen(2)).
Printf places output on the standard output stream stdout. Sprintf
places output followed by the null character (\0) in consecutive
bytes starting at s; it is the user's responsibility to ensure
that enough storage is available. Snprintf is like sprintf but
writes at most n bytes (including the null character) into s.
Vfprintf, vprintf, vsnprintf, and vsprintf are the same, except
the args argument is the argument list of the calling function,
and the effect is as if the calling function's argument list from
that point on is passed to the printf routines.
Each function returns the number of characters transmitted (not
including the \0 in the case of sprintf and friends), or a negative
value if an output error was encountered.
These functions convert, format, and print their trailing arguments
under control of a format string. The format contains two types
of objects: plain characters, which are simply copied to the output
stream, and conversion specifications, each of which results in
fetching of zero or more arguments. The results are
undefined if there are arguments of the wrong type or too few
arguments for the format. If the format is exhausted while arguments
remain, the excess are ignored.
Each conversion specification is introduced by the character %.
After the %, the following appear in sequence:
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Zero or more flags, which modify the meaning of the conversion
specification.
An optional decimal digit string specifying a minimum field width.
If the converted value has fewer characters than the field width,
it will be padded with spaces on the left (or right, if the left
adjustment, described later, has been given) to the field width.
An optional precision that gives the minimum number of digits
to appear for the d, i, o, u, x, and X conversions, the number
of digits to appear after the decimal point for the e, E, and
f conversions, the maximum number of significant digits for the
g and G conversions, or the maximum number of characters
to be written from a string in s conversion. The precision takes
the form of a period (.) followed by an optional decimal integer;
if the integer is omitted, it is treated as zero.
An optional h specifying that a following d, i, o, u, x or X conversion
specifier applies to a short int or unsigned short argument (the
argument will have been promoted according to the integral promotions,
and its value shall be converted to short or unsigned short before
printing); an optional
h specifying that a following n conversion specifier applies to
a pointer to a short argument; an optional l (ell) specifying
that a following d, i, o, u, x, or X conversion character applies
to a long or unsigned long argument; an optional l specifying
that a following n conversion specifier applies to a
pointer to a long int argument; or an optional L specifying 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.
A character that indicates the type of conversion to be applied.
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A field width or precision, or both, may be indicated by an asterisk
(*) instead of a digit string. In this case, an int arg supplies
the field width or precision. The arguments specifying field width
or precision, or both, shall appear (in that order) before the
argument (if any) to be converted. A negative field width
argument is taken as a – flag followed by a positive field width.
A negative precision is taken as if it were missing.
The flag characters and their meanings are:
– The result of the conversion is left–justified within the field.
+ The result of a signed conversion always begins with a sign (+
or –).
blank If the first character of a signed conversion is not a sign,
or a signed conversion results in no characters, a blank is prefixed
to the result. This implies that if the blank and + flags both
appear, the blank flag is ignored.
# The result is to be converted to an ``alternate form.'' For o
conversion, it increases the precision to force the first digit
of the result to be a zero. For x or X conversion, a non–zero result
has 0x or 0X prefixed to it. For e, E, f, g, and G conversions,
the result always contains a decimal point, even if no digits
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follow the point (normally, a decimal point appears in the result
of these conversions only if a digit follows it). For g and G
conversions, trailing zeros are not be removed from the result
as they normally are. For other conversions, the behavior is undefined.
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0 For d, i, o, u, x, X, e, E, f, g, and G conversions, leading
zeros (following any indication of sign or base) are used to pad
the field width; no space padding is performed. If the 0 and –
flags both appear, the 0 flag will be ignored. For d, i, o, u,
x, and X conversions, if a precision is specified, the 0 flag
will
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be ignored. For other conversions, the behavior is undefined.
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The conversion characters and their meanings are:
d,o,u,x,X
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The integer arg is converted to signed decimal (d or i), unsigned
octal (o), unsigned decimal (u), or unsigned hexadecimal notation
(x or X); the letters abcdef are used for x conversion and the
letters ABCDEF for X conversion. The precision specifies the minimum
number of digits to appear; if the value
being converted can be represented in fewer digits, it is expanded
with leading zeros. The default precision is 1. The result of
converting a zero value with a precision of zero is no characters.
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f The double argument is converted to decimal notation in the style
[–]ddd.ddd, where the number of digits after the decimal point
is equal to the precision specification. If the precision is missing,
it is taken as 6; if the precision is explicitly 0, no decimal
point appears.
e,E The double argument is converted in the style [–]d.ddde±dd, where
there is one digit before the decimal point and the number of
digits after it is equal to the precision; when the precision
is missing, it is taken as 6; if the precision is zero, no decimal
point appears. The E format code produces a number
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with E instead of e introducing the exponent. The exponent always
contains at least two digits.
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g,G The double argument is printed in style f or e (or in style
E in the case of a G conversion specifier), with the precision
specifying the number of significant digits. If an explicit precision
is zero, it is taken as 1. The style used depends on the value
converted: style e is used only if the exponent resulting
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from the conversion is less than –4 or greater than or equal to
the precision. Trailing zeros are removed from the fractional
portion of the result; a decimal point appears only if it is followed
by a digit.
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c The int argument is converted to an unsigned char, and the resulting
character is written.
s The argument is taken to be a string (character pointer) and
characters from the string are printed until a null character
(\0) is encountered or the number of characters indicated by the
precision specification is reached. If the precision is missing,
it is taken to be infinite, so all characters up to the first
null
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character are printed. A zero value for the argument yields undefined
results.
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P The void* argument is printed in an implementation–defined way
(for Plan 9: the address as hexadecimal number).
n The argument shall be a pointer to an integer into which is written
the number of characters written to the output stream so far by
this call to fprintf. No argument is converted.
% Print a %; no argument is converted.
If a conversion specification is invalid, the behavior is undefined.
If any argument is, or points to, a union or an aggregate (except
for an array of character type using %s conversion, or a pointer
cast to be a pointer to void using %P conversion), the behavior
is undefined.
In no case does a nonexistent or small field width cause truncation
of a field; if the result of a conversion is wider than the field
width, the field is expanded to contain the conversion result.
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