printf(3S) printf(3S)
NAME
printf(), fprintf(), sprintf(), snprintf() - print formatted output
SYNOPSIS
DESCRIPTION
places output on the standard output stream stdout.
places output on the named output stream.
places "output", followed by the null character in consecutive bytes starting at It is the user's responsibility to ensure that enough
storage is available.
behaves like except that it limits the number of characters written to the destination buffer to maxsize, including the terminating null
character.
Each function converts, formats, and prints its args under control of the format. format is a character string containing two types of
objects: plain characters that are copied to the output stream, and conversion specifications, each of which results in fetching zero or
more args. The results are undefined if there are insufficient args for the format. If the format is exhausted while args remain, excess
args are ignored.
Each conversion specification is introduced by the character or where n is a decimal integer in the range 1 through is defined in The con-
struction indicates that this conversion should be applied to the nth argument, rather than to the next unused one.
An argument can be referenced by a specification more than once. The two forms of introducing a conversion specification, and cannot be
mixed within a single format string. When numbered argument specifications are used, specifying the Nth argument requires that all the
leading arguments, from the first to the (N-1)th, are specified in the format string. The results of mixing numbered and unnumbered argu-
ment specifications in a format string are undefined.
After the or the following appear in sequence:
1. Zero or more flags, which modify the meaning of the conversion specification.
2. An optional string of decimal digits to specify a minimum field width in bytes. If the converted value has fewer characters
than the field width, it is be padded on the left (or right, if the left-adjustment flag described below, has been given) to
the field width. If the field width is preceded by a zero, the string is right adjusted with zero-padding on the left (see the
leading-zero flag, described below).
3. A precision that gives the minimum number of digits to appear for the or conversions, the number of digits to appear after the
radix character for the and conversions, the maximum number of significant digits for the conversion, or the maximum number of
bytes to be printed from a string in the conversion. The precision takes the form of a period followed by a decimal digit
string; a null digit string is treated as zero.
4. Zero or more of the following optional character specifications:
o an optional specifying that a following or conversion character applies to a short integer arg
o an optional specifying that a following conversion character applies to a pointer to a short integer arg
o an optional specifying that a following or conversion specifier applies to a signed char or unsigned char argument (the
argument will have been promoted according to the integer promotions, but its value will be converted to short or
unsigned short before printing)
o an optional specifying that a following conversion specifier applies to a pointer to a signed char argument
o an optional specifying that a following or conversion wide-character applies to a type which is the 80-bit IEEE-754 dou-
ble-extended type in the architecture
o an optional specifying that a following or conversion specifier applies to an intmax_t or uintmax_t argument
o an optional specifying that a following conversion specifier applies to a pointer to an intmax_t argument
o an optional (the letter "ell"), specifying that a following or conversion character applies to a long integer arg
o an optional specifying that a following conversion character applies to a pointer to a long integer arg
o an optional specifying that a following or conversion character applies to a long double
o an optional specifying that a following or conversion character applies to a long long integer arg
o an optional specifying that a following or conversion specifier applies to a ptrdiff_t or the corresponding unsigned
type argument
o an optional specifying that a following conversion specifier applies to a pointer to a ptrdiff_t argument
o an optional specifying that a following or conversion specifier applies to a size_t argument or the corresponding signed
integer type argument
o an optional specifying that a following conversion specifier applies to a pointer to a size_t argument arg.
For Itanium(R)-based systems if the optional decimal floating point feature is installed and enabled, the following optional
character specifications are allowed:
o an optional specifying that a following or conversion specifier applies to a argument.
o an optional specifying that a following or conversion specifier applies to a argument.
o an optional specifying that a following or conversion specifier applies to a argument.
5. An or before any other conversion character is ignored.
6. A conversion character that indicates the type of conversion to be applied.
A field width or precision can be indicated by an asterisk instead of a digit string. In this case, an integer arg supplies the field
width or precision. The arg that is actually converted is not fetched until the conversion letter is seen, so the args specifying field
width, or precision, or both must appear in that order before the arg, if any, to be converted. A negative field width is taken as a flag
followed by a positive field width. A negative precision is taken as if the precision were omitted. Format strings containing conversion
specifications can also indicate a field width or precision by the sequence The n indicates the position of an integer arg. With the
sequence, the args specifying field width or precision can appear before or after the arg to be converted.
The flag characters and their meanings are:
The integer portion of the result of a decimal conversion (%i, %d, %u, %f,
%F, %g, or %G) will be formatted with thousands' grouping characters. Thousands' grouping and the separator character are
determined by the "grouping" and "thousands_sep" fields of the category respectively. (See localedef(4)). For other con-
versions the behavior is undefined. The nonmonetary grouping character is used.
The resulting conversion is left-justified within the field.
The resulting signed conversion always begins with a sign
or
blank If the first character of a signed conversion is not a sign, a blank is prefixed to the result. This implies that if the
blank and flags both appear, the blank flag is ignored.
This flag specifies that the value is converted to an "alternate form".
For and conversions, the flag has no effect. For conversion, it increases the precision to force the first digit of the
result to be a zero. For or conversion, a nonzero result is prefixed by or For a conversion, a nonzero result is prefixed
by For and conversions, the result always contains a radix character, even if no digits follow the radix. (Normally, a
radix character appears in the resulting conversions only if followed by a digit). For and conversions, trailing zeros
are removed from the result (which they normally are).
Leading zeros (following any indication of sign or base)
are used to pad to the field width for all conversion characters. No space padding is performed. If both the and appear,
the flag is ignored. For and conversions, if a precision is specified, the flag is ignored.
The conversion characters and their meanings are:
The integer arg is converted to signed decimal and are identical), unsigned octal decimal or hexadecimal notation and respec-
tively; the letters are used for conversion and the letters for conversion. The precision specifies the minimum num-
ber of digits to appear. If the value being converted can be represented in fewer digits, it is expanded with lead-
ing zeros. (For compatibility with older versions, padding with leading zeros can alternatively be specified by
inserting a zero in front of the field width. This does not imply an octal value for the field width). The default
precision is 1. The result of converting a zero value with a precision of zero is a null string.
The double arg is converted to decimal notation in the style where r is the radix character. The number of digits after the
radix character is equal to the precision specification. If the precision is missing, six digits are output. If the
precision is explicitly zero, no radix character appears.
The double arg is converted in the style where is the radix character. There is one digit before the radix character and the
number of digits after it is equal to the precision. When the precision is missing, six digits are produced. If the
precision is zero, no radix character appears. The format code produces a number with instead of introducing the
exponent. The exponent always contains at least two digits.
The double arg is printed in style or (or in style in the case of a format code), with the precision specifying the number of
significant digits. The style used depends on the value converted: style is used only if the exponent resulting from
the conversion is less than or greater than or equal to the precision. Trailing zeros are removed from the frac-
tional part of the result; a radix character appears only if it is followed by a digit.
For Itanium(R)-based systems only.
The double arg is converted in the style where is the radix character. There is one digit before the radix character
and the number of digits after it is equal to the precision. When the precision is missing, 13 digits are produced
for 15 for and 28 for (which is sufficient for an exact representation of the value). If the precision is 0, no
radix character appears. The letters are used for conversion and the letters for conversion. The conversion speci-
fier produces a number with and instead of and The exponent always contains at least one digit, and only as many more
digits as necessary to represent the decimal exponent of 2. If the value is zero, the exponent is zero.
For Itanium(R)-based systems if the optional decimal floating point feature is installed and enabled, then for an or
specifier, if an or modifier is present and the precision is missing, then for a decimal floating type argument rep-
resented with an integral coefficient c and quantum exponent q, where n is the number of digits in the coefficient c:
o If 0 >= q >= -(n+5), use style formatting with formatting precision equal to -q.
o Otherwise, use style formatting with formatting precision equal to n - 1. Except if then the digit-sequence
in the exponent-part will have the value q (rather than 0), and that the exponent is always expressed with the
minimum number of digits required to represent its value (the exponent never contains a leading zero).
If the precision modifier is present and at least as large as the precision of the decimal floating type, the conver-
sion is as if the precision modifier were missing.
If the precision modifier is present and less than the precision of the decimal floating type, the conversion first
rounds the input, in the type, according to the current rounding direction for decimal floating-point operations.
The rounding occurs to the number of digits specified by the precision modifier, then converts the result as if the
precision modifier were missing.
The integer arg is converted to an unsigned char, and the resulting character is printed. If an (ell) qualifier is present, the
arg is converted to an array of bytes representing the single wide character according to the setting of Resulting
bytes are printed. If the field width would otherwise cause the wide character to be split, the wide character is
printed and the field width is adjusted upward.
only: If an (ell) qualifier is present, the argument is converted as if by an conversion specification with no preci-
sion and an argument that points to a two-element array of type the first element of which contains the argument to
the conversion specification and the second element contains a null wide-character.
Same as
The arg is taken to be a string (character pointer) and characters from the string are printed until a null character is
encountered or the number of bytes 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 character are printed. A NULL value for arg
yields undefined results.
If an (ell) qualifier is present, the argument must be a pointer to an array of type Wide-characters from the array
are converted to characters (each as if by a call to the function, with the conversion state described by an object
initialized to zero before the first wide-character is converted) up to and including a terminating null wide-charac-
ter. The resulting characters are written up to (but not including) the terminating null character (byte).
If no precision is specified, the array must contain a null wide-character. If a precision is specified, no more
than that many characters (bytes) are written (including shift sequences, if any), and the array must contain a null
wide-character if, to equal the character sequence length given by the precision, the function would need to access a
wide-character one past the end of the array. In no case is a partial character written.
Same as
The value of a pointer to void
arg is printed as a sequence of unsigned hexadecimal numbers. 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 a null string.
A pointer to an integer
arg is expected. This pointer is used to store the number of bytes printed on the output stream so far by this call
to the function. No argument is converted.
Print a no argument is converted. The entire conversion specification must be
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.
The and conversions will print for infinity and for both quiet and signaling values.
The and conversions will print for infinity and for both quiet and signaling values.
For and conversions (on Itanium(R)-based systems), the value is correctly rounded to a hexadecimal floating point number with the given
precision.
The and conversions on Itanium(R)-based systems round according to the specification in ISO/IEC C99: if the number of significant decimal
digits is at most 36, then the result is correctly rounded.
Characters generated by and are printed as if had been called (see putc(3S)).
For Itanium(R)-based systems if the optional decimal floating point feature is installed and enabled, the behavior of the and specifiers
for decimal floating point numbers is the same as for
Application Usage
To use the functionality, the flag must be passed as a compiler option or defined as a macro in source files.
After or is applied to a stream, the stream becomes byte-oriented (see orientation(5)).
EXTERNAL INFLUENCES
Environment Variables
The category affects the following features:
o Plain characters within format strings are interpreted as single byte and/or multibyte characters.
o Field width is given in terms of bytes. As characters are placed on the output stream, they are interpreted as single byte or multi-
byte characters and the field width is decremented by the length of the character.
o Precision is given in terms of bytes. As characters are placed on the output stream, they are interpreted as single byte or multibyte
characters and the precision is decremented by the length of the character.
o The return value is given in terms of bytes. As characters are placed on the output stream, they are interpreted as single byte or
multibyte characters and the byte count that makes up the return value is incremented by the length of the character.
The category determines the radix character used to print floating-point numbers, and the thousands' grouping characters if the grouping
flag is on.
International Code Set Support
Single byte character code sets are supported. Multibyte character code sets are also supported as described in the category above.
RETURN VALUE
Each function returns the number of bytes transmitted (excluding the null character in the case of or a negative value if an output error
was encountered.
By default, returns a negative value if maxsize is smaller than the number of characters formatted. In the UNIX 2003 standards environment
(see standards(5)) it returns the the number of bytes that would have been written to buffer s, excluding the terminating null byte, if
maxsize had been sufficiently large.
ERRORS
and fail if either the stream is unbuffered or stream's buffer needed to be flushed causing an underlying call to be invoked (see
write(2)), and:
The flag is set for the file descriptor underlying stream and the process would be delayed in the write operation.
The file descriptor underlying
stream is not a valid file descriptor open for writing.
An attempt was made to write to a file that exceeds the process's file size
limit or the maximum file size (see ulimit(2)).
A signal was caught during the
system call.
The process is in a background process group
and is attempting to write to its controlling terminal, is set, the process is neither ignoring nor blocking the signal, and
the process group of the process is orphaned.
There was no free space remaining on the device containing the file.
An attempt is made to write to a pipe or
FIFO that is not open for reading by any process. A signal is also sent to the process.
The data obtained from the input stream does not form a valid wide character.
Insufficient storage space is available.
Additional values can be set by the underlying function (see write(2)).
EXAMPLES
To print a date and time in the form "Sunday, July 3, 10:02", where weekday and month are pointers to null-terminated strings:
To print Pi to 5 decimal places:
To create a language independent date-and-time printing routine write:
For American usage, format would point to the string:
and result in the output:
For German usage, the string:
results in the output:
WARNINGS
Notice that with the conversion character, an int arg is converted to an unsigned char. Hence, whole multibyte characters cannot be
printed using a single conversion character.
A precision with the conversion character might result in the truncation of a multibyte character.
Use of a conversion character which doesn't match the type of the corresponding argument passed in will result in invalid data being
returned. For example, the modifying specifying that the following or conversion character applies to a long long integer arg, is neces-
sary for proper results when the argument is a long long integer.
AUTHOR
and were developed by AT&T and HP.
SEE ALSO
ecvt(3C), ltostr(3C), setlocale(3C), putc(3S), scanf(3S), stdio(3S), orientation(5), standards(5), thread_safety(5), glossary(9).
STANDARDS CONFORMANCE
printf(3S)