printf format [arguments…]
utility† formats and outputs its arguments, under control of the format.
format string contains
plain characters, which are simply copied to standard output,
- escape sequences which are converted and copied to the standard output, and
- format specifications causes outputing of the next successive argument.
The arguments after the first are treated as strings if the corresponding format is either
c, b or s
; otherwise it is evaluated as a C language constant, except that:
- leading plus or minus sign is allowed.
- leading apostrophe or quote causes the value is the ASCII code of the next character.
format is reused as often as necessary to satisfy the arguments.
Excess format specifications are evaluated with zero or null .
Escape sequences are in backslash notation
\b <backspace> \t <tab>
\f <form-feed> \v <vertical tab>
\n <new-line> \r <return>
\0num Write an 8-bit character whose ASCII value is the 1-3 digit octal number num.
\a <alert bell>
\c Ignore remaining characters
format is introduced by
% followed by, in order:
Zero or more flags:
| left adjustment
| always output a sign
| space should be left before a positive number for a signed format. ( A |
+ overrides a space)
| zero padding <.br>
A `-' overrides a `0'
| alternate form:|
o : the precision is increased to force a leading zero.
X) : a non-zero has
0X) prepended .
e, E, f, g, and G , the result always contains a decimal (normally, a decimal appears if a digit follows ).
G : trailing zeros are not removed
s has no effect.
A field width or precision may be `*' instead of a digit string. In this case an argument supplies the
field width or precision.
The format characters and their meanings are:
An optional digit string specifying a field width; if the output string has fewer characters
than the field width it will be blank-padded on the left (or right, if the left-adjustment
indicator has been given) to make up the field width (note that a leading zero is a flag, but
an embedded zero is part of a field width);
An optional period, `.', followed by an optional digit string giving a precision which specifies the number of digits to appear after the decimal point, for e and f formats, or the maximum number of characters to be printed from a string; if the digit string is missing, the precision is treated as zero;
A character which indicates the type of format to use (one of |
The uppercase formats differ from their lowercase counterparts only in that the output of the former is
entirely in uppercase.
The floating-point format specifiers (
fFeEgGaA) may be prefixed by an
to request that additional precision be used, if available.
di o u Xx
| The argument is printed as a signed decimal (d or i), unsigned octal, unsigned decimal, or
unsigned hexadecimal (X or x)
| [-]ddd.ddd' where the number of d's after the decimal
point is equal to the precision specification for the argument.
If the precision not given, 6 digits are given; if the precision is explicitly 0, no digits and no decimal point
are printed. |
The values infinity and NaN(NotANumber) are printed as inf and nan
| e `[-d.ddd+-dd] where there is one digit before the
decimal point and the number after is equal to the precision specification for the argu-
ment; when the precision is missing, 6 digits are produced. The values infinity and NaN
are printed as `inf' and `nan', respectively.
| f (F) or e (E) whichever gives full precision in minimum space.
| [-h.hhh+-pd] where there is one digit before the hexadecimal point and
the number after is equal to the precision specification for the argument; when the precision is missing, enough digits are produced to convey the argument's
exact double-precision floating-point representation.|
The values infinity and NaN are printed as `inf' and `nan', respectively.
| only first character of argument is printed.
| Characters from the string argument are output until the end is reached or until the number of characters indicated by the precision specification is reached; however if the precision is 0 or missing, all characters in the string are printed.
| As for |
s, but interpret character escapes in backslash notation in the string argument.
| output a |
%; no argument is used.
The decimal point character is defined in the program's locale (category LC_NUMERIC).
In no case does a non-existent or small field width cause truncation of a field;
padding takes place only if the specified field width exceeds the actual width.
The printf utility exits 0 on success, and >0 if an error occurs.
The traditional BSD behavior of converting arguments of numeric formats not beginning with a digit to
the ASCII code of the first character is not supported.
The printf command is expected to be mostly compatible with the IEEE Std 1003.2 (``POSIX.2'') specification.
Since the floating point numbers are translated from ASCII to floating-point and then back again,
floating-point precision may be lost. (By default, the number is translated to an IEEE-754 double-precision value before being printed. The L modifier may produce additional precision, depending on the
ANSI hexadecimal character constants were deliberately not provided.
The escape sequence \000 is the string terminator. When present in the argument for the b format, the
argument will be truncated at the \000 character.
Multibyte characters are not recognized in format strings (this is only a problem if `%' can appear
inside a multibyte character).
Parsing of - arguments is also somewhat different from printf(3), where unknown arguments are simply
printed instead of being flagged as errors.