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curl/docs/libcurl/curl_mprintf.3
Daniel Stenberg e2497c73f9
curl_mprintf.3: add description 
These functions have existed in the API since the dawn of time. It is
about time we describe how they work, even if we discourage users from
using them.

Closes #7010
2021-05-06 23:21:12 +02:00

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.\" **************************************************************************
.\" * _ _ ____ _
.\" * Project ___| | | | _ \| |
.\" * / __| | | | |_) | |
.\" * | (__| |_| | _ <| |___
.\" * \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
.\" * are also available at https://curl.se/docs/copyright.html.
.\" *
.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
.\" * copies of the Software, and permit persons to whom the Software is
.\" * furnished to do so, under the terms of the COPYING file.
.\" *
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
.\" * KIND, either express or implied.
.\" *
.\" **************************************************************************
.TH curl_printf 3 "30 April 2004" "libcurl 7.12" "libcurl Manual"
.SH NAME
curl_maprintf, curl_mfprintf, curl_mprintf, curl_msnprintf, curl_msprintf
curl_mvaprintf, curl_mvfprintf, curl_mvprintf, curl_mvsnprintf,
curl_mvsprintf - formatted output conversion
.SH SYNOPSIS
.B #include <curl/mprintf.h>
.sp
.BI "int curl_mprintf(const char *" format ", ...);"
.br
.BI "int curl_mfprintf(FILE *" fd ", const char *" format ", ...);"
.br
.BI "int curl_msprintf(char *" buffer ", const char *" format ", ...);"
.br
.BI "int curl_msnprintf(char *" buffer ", size_t " maxlength ", const char *" format ", ...);"
.br
.BI "int curl_mvprintf(const char *" format ", va_list " args ");"
.br
.BI "int curl_mvfprintf(FILE *" fd ", const char *" format ", va_list " args ");"
.br
.BI "int curl_mvsprintf(char *" buffer ", const char *" format ", va_list " args ");"
.br
.BI "int curl_mvsnprintf(char *" buffer ", size_t " maxlength ", const char *" format ", va_list " args ");"
.br
.BI "char *curl_maprintf(const char *" format ", ...);"
.br
.BI "char *curl_mvaprintf(const char *" format ", va_list " args ");"
.SH DESCRIPTION
These functions produce output according to the format string and given
arguments. They are mostly clones of the well-known C-style functions but
there are slight differences in behavior.
We discourage users from using any of these functions in new applications.
Functions in the curl_mprintf() family produce output according to a format as
described below. The functions \fBcurl_mprintf()\fP and \fBcurl_mvprintf()\fP
write output to stdout, the standard output stream; \fBcurl_mfprintf()\fP and
\fBcurl_mvfprintf()\fP write output to the given output stream;
\fBcurl_msprintf()\fP, \fBcurl_msnprintf()\fP, \fBcurl_mvsprintf()\fP, and
\fBcurl_mvsnprintf()\fP write to the character string \fBbuffer\fP.
The functions \fBcurl_msnprintf()\fP and \fBcurl_mvsnprintf()\fP write at most
\fImaxlength\fP bytes (including the terminating null byte ('\\0')) to
\fIbuffer\fP.
The functions \fBcurl_mvprintf()\fP, \fBcurl_mvfprintf()\fP,
\fBcurl_mvsprintf()\fP, \fBcurl_mvsnprintf()\fP are equivalent to the
functions \fBcurl_mprintf()\fP, \fBcurl_mfprintf()\fP, \fBcurl_msprintf()\fP,
\fBcurl_msnprintf()\fP, respectively, except that they are called with a
va_list instead of a variable number of arguments. These functions do not
call the va_end macro. Because they invoke the va_arg macro, the value of ap
is undefined after the call.
The functions \fBcurl_maprintf()\fP and \fBcurl_mvaprintf()\fP return the
output string as pointer to a newly allocated memory area. The returned string
must be \fIcurl_free(3)\fPed by the receiver.
All of these functions write the output under the control of a format string
that specifies how subsequent arguments are converted for output.
.SH FORMAT STRING
The format string is composed of zero or more directives: ordinary characters
(not %), which are copied unchanged to the output stream; and conversion
specifications, each of which results in fetching zero or more subsequent
arguments. Each conversion specification is introduced by the character %, and
ends with a conversion specifier. In between there may be (in this order) zero
or more \fIflags\fP, an optional minimum \fIfield width\fP, an optional
\fIprecision\fP and an optional \fIlength modifier\fP.
.SH "The $ modifier"
The arguments must correspond properly with the conversion specifier. By
default, the arguments are used in the order given, where each '*' (see Field
width and Precision below) and each conversion specifier asks for the next
argument (and it is an error if insufficiently many arguments are given). One
can also specify explicitly which argument is taken, at each place where an
argument is required, by writing "%m$" instead of '%' and "*m$" instead
of '*', where the decimal integer m denotes the position in the argument list
of the desired argument, indexed starting from 1. Thus,
curl_mprintf("%*d", width, num);
and
curl_mprintf("%2$*1$d", width, num);
are equivalent. The second style allows repeated references to the same
argument.
If the style using '$' is used, it must be used throughout for all conversions
taking an argument and all width and precision arguments, but it may be mixed
with "%%" formats, which do not consume an argument. There may be no gaps in
the numbers of argu‐ ments specified using '$'; for example, if arguments 1
and 3 are specified, argument 2 must also be specified somewhere in the format
string.
.SH "Flag characters"
The character % is followed by zero or more of the following flags:
.TP
.B #
The value should be converted to its "alternate form".
.TP
.B 0
The value should be zero padded.
.TP
.B -
The converted value is to be left adjusted on the field boundary. (The
default is right justification.) The converted value is padded on the right
with blanks, rather than on the left with blanks or zeros. A '-' overrides a
\&'0' if both are given.
.TP
.B ' '
(a space) A blank should be left before a positive number (or empty string)
produced by a signed conversion.
.TP
.B +
A sign (+ or -) should always be placed before a number produced by a signed
conversion. By default, a sign is used only for negative numbers. A '+'
overrides a space if both are used.
.SH "Field width"
An optional decimal digit string (with nonzero first digit) 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 flag has been given). Instead of a decimal digit string one
may write "*" or "*m$" (for some decimal integer m) to specify that the field
width is given in the next argument, or in the m-th argument, respec‐ tively,
which must be of type int. A negative field width is taken as a '-' flag
followed by a positive field width. In no case does a nonexistent or small
field width cause truncation of a field; if the result of a conversion is
wider than the field width, the field is expanded to contain the conversion
result.
.SH "Precision"
An optional precision in the form of a period ('.') followed by an optional
decimal digit string. Instead of a decimal digit string one may write "*" or
"*m$" (for some decimal integer m) to specify that the precision is given in
the next argument, or in the m-th argument, respectively, which must be of
type int. If the precision is given as just '.', the precision is taken to be
zero. A negative precision is taken as if the precision were omitted. This
gives the minimum number of digits to appear for \fBd\fP, \fBi\fP, \fBo\fP,
\fBu\fP, \fBx\fP, and \fBX\fP conversions, the number of digits to appear
after the radix character for \fBa\fP, \fBA\fP, \fBe\fP, \fBE\fP, \fBf\fP, and
\fBF\fP conversions, the maximum number of significant digits for \fBg\fP and
\fBG\fP conversions, or the maximum number of characters to be printed from a
string for \fBs\fP and \fBS\fP conversions.
.SH "Length modifier"
.TP
.B h
A following integer conversion corresponds to a \fIshort\fP or \fIunsigned
short\fP argument.
.TP
.B l
(ell) A following integer conversion corresponds to a \fIlong\fP or
\fIunsigned long\fP argument, or a following n conversion corresponds to a
pointer to a long argument
.TP
.B ll
(ell-ell). A following integer conversion corresponds to a \fIlong long\fP or
\fIunsigned long long\fP argument, or a following n conversion corresponds to
a pointer to a long long argument.
.TP
.B q
A synonym for \fBll\fP.
.TP
.B L
A following a, A, e, E, f, F, g, or G conversion corresponds to a long double
argument.
.TP
.B z
A following integer conversion corresponds to a \fIsize_t\fP or \fIssize_t\fP
argument.
.SH "Conversion specifiers"
A character that specifies the type of conversion to be applied. The
conversion specifiers and their meanings are:
.TP
.B d, i
The int argument is converted to signed decimal notation. The precision, if
any, gives the minimum number of digits that must appear; if the converted
value requires fewer digits, it is padded on the left with zeros. The default
precision is 1. When 0 is printed with an explicit precision 0, the output is
empty.
.TP
.B o, u, x, X
The unsigned int argument is converted to unsigned octal (o), unsigned decimal
(u), or unsigned hexadecimal (\fBx\fP and \fBX\fP) notation. The letters
abcdef are used for \fBx\fP conversions; the letters ABCDEF are used for
\fBX\fP conversions. The precision, if any, gives the minimum number of digits
that must appear; if the converted value requires fewer digits, it is padded
on the left with zeros. The default precision is 1. When 0 is printed with
an explicit precision 0, the output is empty.
.TP
.B e, E
The double argument is rounded and output in the style "[-]d.ddde±dd"
.TP
.B f, F
The double argument is rounded and output to decimal notiation in the style
[-]ddd.ddd.
.TP
.B g, G
The double argument is converted in style f or e.
.TP
.B c
The int argument is converted to an unsigned char, and the resulting character
is written.
.TP
.B s
The const char * argument is expected to be a pointer to an array of character
type (pointer to a string). Characters from the array are written up to (but
not including) a terminating null byte. If a precision is specified, no more
than the number specified are written. If a precision is given, no null byte
need be present; if the precision is not specified, or is greater than the
size of the array, the array must contain a terminating null byte.
.TP
.B p
The \fIvoid *\fP pointer argument is printed in hexadecimal.
.TP
.B n
The number of characters written so far is stored into the integer pointed to
by the corresponding argument.
.TP
.B %
A '%' is written. No argument is converted.
.SH AVAILABILITY
These functions will be removed from the public libcurl API in the future. Do
not use them in new programs or projects.
.SH RETURN VALUE
The \fBcurl_maprintf\fP and \fBcurl_mvaprintf\fP functions return a pointer to
a newly allocated string, or NULL if it failed.
All other functions return the number of characters they actually
outputted. Note that this differs from how the POSIX versions of these
functions work.
.SH "SEE ALSO"
.BR printf "(3), " sprintf "(3), " fprintf "(3), " vprintf "(3) "
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