\HeaderA{sprintf}{Use C-style String Formatting Commands}{sprintf}
\aliasA{gettextf}{sprintf}{gettextf}
\keyword{print}{sprintf}
\keyword{character}{sprintf}
\begin{Description}\relax
A wrapper for the C function \code{sprintf}, that returns a character
vector containing a formatted combination of text and variable values.
\end{Description}
\begin{Usage}
\begin{verbatim}
sprintf(fmt, ...)
gettextf(fmt, ..., domain = NULL)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{fmt}] a character vector of format strings, each of up to 8192 bytes.
\item[\code{...}] values to be passed into \code{fmt}.  Only logical,
integer, real and character vectors are supported, but some coercion
will be done: see the \sQuote{Details} section.
\item[\code{domain}] see \code{\LinkA{gettext}{gettext}}.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
\code{sprintf} is a wrapper for the system \code{sprintf} C-library
function.  Attempts are made to check that the mode of the values
passed match the format supplied, and \R's special values (\code{NA},
\code{Inf}, \code{-Inf} and \code{NaN}) are handled correctly.

\code{gettextf} is a convenience function which provides C-style
string formatting with possible translation of the format string.

The arguments (including \code{fmt}) are recycled if possible a whole
number of times to the length of the longest, and then the formatting
is done in parallel.  As from \R{} 2.9.0 zero-length arguments are
allowed and will give a zero-length result.  All arguments are
evaluated even if unused, and hence some types (e.g., \code{"symbol"}
or \code{"language"}, see \code{\LinkA{typeof}{typeof}}) are not allowed.

The following is abstracted from Kernighan and Ritchie
(see References).  The string \code{fmt} contains normal characters,
which are passed through to the output string, and also conversion
specifications which operate on the arguments provided through
\code{...}.  The allowed conversion specifications start with a
\code{\%} and end with one of the letters in the set
\code{difeEgGsxXaA\%}.  These letters denote the following types:

\describe{
\item[\code{d, i, x, X}] Integer value, \code{x} and \code{X}
being hexadecimal (using the same case for \code{a-f} as the code).
Numeric variables with exactly integer values will be coerced to
integer. Formats \code{d} and \code{i} can also be used for
logical variables, which will be converted to \code{0}, \code{1}
or \code{NA}.

\item[\code{f}] Double precision value, in \dQuote{\bold{f}ixed
point} decimal notation of the form "[-]mmm.ddd".  The number of
decimal places ("d") is specified by the precision: the default is 6;
a precision of 0 suppresses the decimal point.  Non-finite values
are converted to \code{NA}, \code{NaN} or (perhaps a sign followed
by) \code{Inf}.

\item[\code{e, E}] Double precision value, in
\dQuote{\bold{e}xponential} decimal notation of the
form \code{[-]m.ddde[+-]xx} or \code{[-]m.dddE[+-]xx}.

\item[\code{g, G}] Double precision value, in \code{\%e} or
\code{\%E} format if the exponent is less than -4 or greater than or
equal to the precision, and \code{\%f} format otherwise.
(The precision (default 6) specifies the number of
\emph{significant} digits here, whereas in \code{\%f, \%e}, it is
the number of digits after the decimal point.)

\item[\code{a, A}] Double precision value, in binary notation of the
form \code{[-]0xh.hhhp[+-]d}.  This is a binary fraction
expressed in hex multiplied by a (decimal) power of 2.  The number
of hex digits after the decimal point is specified by the precision:
the default is enough digits to represent exactly the internal
binary representation.  Non-finite values are converted to \code{NA},
\code{NaN} or (perhaps a sign followed by) \code{Inf}.  Format
\code{\%a} uses lower-case for \code{x}, \code{p} and the hex
values: format \code{\%A} uses upper-case.

This might not be supported on all platforms as it is a feature of C99.
The format is not uniquely defined: although it would be possible
to make the leading \code{h} always zero or one, this is not
always done.  Most systems will suppress trailing zeros, but a few
do not.  On a well-written platform, for normal numbers there will
be a leading one before the decimal point plus (by default) 13
hexadecimal digits, hence 53 bits.  (The treatment of denormalized
numbers is very platform-dependent.)

\item[\code{s}] Character string.  Character \code{NA}s are
converted to \code{"NA"}.

\item[\code{\%}] Literal \code{\%} (none of the extra formatting
characters given below are permitted in this case).

}
Conversion by \code{\LinkA{as.character}{as.character}} is used for non-character
arguments with \code{s} and by \code{\LinkA{as.double}{as.double}} for
non-double arguments with \code{f, e, E, g, G}.  NB: the length is
determined before conversion, so do not rely on the internal
coercion if this would change the length.  The coercion is done only
once, so if \code{length(fmt) > 1} then all elements must expect the
same types of arguments.

In addition, between the initial \code{\%} and the terminating
conversion character there may be, in any order:

\describe{
\item[\code{m.n}] Two numbers separated by a period, denoting the
field width (\code{m}) and the precision (\code{n}).
\item[\code{-}] Left adjustment of converted argument in its field.
\item[\code{+}] Always print number with sign: by default only
negative numbers are printed with a sign.
\item[a space] Prefix a space if the first character is not a sign.
\item[\code{0}] For numbers, pad to the field width with leading zeros.
\item[\code{\#}] specifies \dQuote{alternate output} for numbers, its
action depending on the type:
For \code{x} or \code{X}, \code{0x} or \code{0X} will be prefixed
to a non-zero result.  For \code{e}, \code{e}, \code{f}, \code{g}
and \code{G}, the output will always have a decimal point; for
\code{g} and \code{G}, trailing zeros will not be removed.

}
Further, immediately after \code{\%} may come \code{1\$} to \code{99\$}
to refer to numbered argument: this allows arguments to be
referenced out of order and is mainly intended for translators of
error messages.  If this is done it is best if all formats are
numbered: if not the unnumbered ones process the arguments in order.
See the examples.  This notation allows arguments to be used more than
once, in which case they must be used as the same type (integer,
double or character).

A field width or precision (but not both) may be indicated by an
asterisk \code{*}: in this case an argument specifies the desired
number.  A negative field width is taken as a '-' flag followed by a
positive field width.  A negative precision is treated as if the
precision were omitted.  The argument should be integer, but a double
argument will be coerced to integer.

There is a limit of 8192 bytes on elements of \code{fmt}, and on
strings included from a single \code{\%}\emph{letter} conversion
specification.

Field widths and precisions of \code{\%s} conversions are interpreted
as bytes, not characters, as described in the C standard.
\end{Details}
\begin{Value}
A character vector of length that of the longest input.  If any
element of \code{fmt} or any character argument is declared as UTF-8,
the element of the result will be in UTF-8 and have the encoding
declared as UTF-8.  Otherwise it will be in the current locale's
encoding.
\end{Value}
\begin{Section}{Warning}
The format string is passed down the OS's \code{sprintf} function, and
incorrect formats can cause the latter to crash the \R{} process .  \R{}
does perform sanity checks on the format, and since \R{} 2.10.0, we have
not seen crashes anymore.  But not all possible user errors on all
platforms have been tested, and some might be terminal.
\end{Section}
\begin{Author}\relax
Original code by Jonathan Rougier.
\end{Author}
\begin{References}\relax
Kernighan, B. W. and Ritchie, D. M. (1988)
\emph{The C Programming Language.} Second edition, Prentice Hall.
describes the format options in table B-1 in the Appendix.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{formatC}{formatC}} for a way of formatting vectors of numbers in a
similar fashion.

\code{\LinkA{paste}{paste}} for another way of creating a vector combining
text and values.

\code{\LinkA{gettext}{gettext}} for the mechanisms for the automated translation
of text.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
## be careful with the format: most things in R are floats
## only integer-valued reals get coerced to integer.

sprintf("%s is %f feet tall\n", "Sven", 7.1)      # OK
try(sprintf("%s is %i feet tall\n", "Sven", 7.1)) # not OK
    sprintf("%s is %i feet tall\n", "Sven", 7  )  # OK

## use a literal % :

sprintf("%.0f%% said yes (out of a sample of size %.0f)", 66.666, 3)

## various formats of pi :

sprintf("%f", pi)
sprintf("%.3f", pi)
sprintf("%1.0f", pi)
sprintf("%5.1f", pi)
sprintf("%05.1f", pi)
sprintf("%+f", pi)
sprintf("% f", pi)
sprintf("%-10f", pi) # left justified
sprintf("%e", pi)
sprintf("%E", pi)
sprintf("%g", pi)
sprintf("%g",   1e6 * pi) # -> exponential
sprintf("%.9g", 1e6 * pi) # -> "fixed"
sprintf("%G", 1e-6 * pi)

## no truncation:
sprintf("%1.f",101)

## re-use one argument three times, show difference between %x and %X
xx <- sprintf("%1$d %1$x %1$X", 0:15)
xx <- matrix(xx, dimnames=list(rep("", 16), "%d%x%X"))
noquote(format(xx, justify="right"))

## More sophisticated:

sprintf("min 10-char string '%10s'",
        c("a", "ABC", "and an even longer one"))

n <- 1:18
sprintf(paste("e with %2d digits = %.",n,"g",sep=""), n, exp(1))

## Using arguments out of order
sprintf("second %2$1.0f, first %1$5.2f, third %3$1.0f", pi, 2, 3)

## Using asterisk for width or precision
sprintf("precision %.*f, width '%*.3f'", 3, pi, 8, pi)

## Asterisk and argument re-use, 'e' example reiterated:
sprintf("e with %1$2d digits = %2$.*1$g", n, exp(1))

## re-cycle arguments
sprintf("%s %d", "test", 1:3)

## binary output showing rounding/representation errors
x <- seq(0, 1.0, 0.1); y <- c(0,.1,.2,.3,.4,.5,.6,.7,.8,.9,1)
cbind(x, sprintf("%a", x), sprintf("%a", y))
\end{ExampleCode}
\end{Examples}

