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<head>
<title>fmtinstall(3) - Plan 9 from User Space</title>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
</head>
<body bgcolor=#ffffff>
<table border=0 cellpadding=0 cellspacing=0 width=100%>
<tr height=10><td>
<tr><td width=20><td>
<tr><td width=20><td><b>FMTINSTALL(3)</b><td align=right><b>FMTINSTALL(3)</b>
<tr><td width=20><td colspan=2>
<br>
<p><font size=+1><b>NAME </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
fmtinstall, dofmt, dorfmt, fmtprint, fmtvprint, fmtrune, fmtstrcpy,
fmtrunestrcpy, fmtfdinit, fmtfdflush, fmtstrinit, fmtstrflush,
runefmtstrinit, runefmtstrflush, errfmt – support for user-defined
print formats and output routines<br>
</table>
<p><font size=+1><b>SYNOPSIS </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>#include <u.h><br>
#include <libc.h>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>typedef struct Fmt Fmt;<br>
struct Fmt{<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
uchar runes; /* output buffer is runes or chars? */<br>
void *start; /* of buffer */<br>
void *to; /* current place in the buffer */<br>
void *stop; /* end of the buffer; overwritten if flush fails */<br>
int (*flush)(Fmt*);/* called when to == stop */<br>
void *farg; /* to make flush a closure */<br>
int nfmt; /* num chars formatted so far */<br>
va_list args; /* args passed to dofmt */<br>
int r; /* % format Rune */<br>
int width;<br>
int prec;<br>
ulong flags;<br>
</table>
};<br>
enum{<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
FmtWidth = 1,<br>
FmtLeft = FmtWidth << 1,<br>
FmtPrec = FmtLeft << 1,<br>
FmtSharp = FmtPrec << 1,<br>
FmtSpace = FmtSharp << 1,<br>
FmtSign = FmtSpace << 1,<br>
FmtZero = FmtSign << 1,<br>
FmtUnsigned = FmtZero << 1,<br>
FmtShort = FmtUnsigned << 1,<br>
FmtLong = FmtShort << 1,<br>
FmtVLong = FmtLong << 1,<br>
FmtComma = FmtVLong << 1,<br>
FmtFlag = FmtComma << 1<br>
</table>
};<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
int fmtfdinit(Fmt *f, int fd, char *buf, int nbuf);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtfdflush(Fmt *f);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtstrinit(Fmt *f);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>char* fmtstrflush(Fmt *f);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int runefmtstrinit(Fmt *f);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>Rune* runefmtstrflush(Fmt *f);<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtinstall(int c, int (*fn)(Fmt*));
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int dofmt(Fmt *f, char *fmt);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int dorfmt(Fmt*, Rune *fmt);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtprint(Fmt *f, char *fmt, ...);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtvprint(Fmt *f, char *fmt, va_list v);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtrune(Fmt *f, int r);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtstrcpy(Fmt *f, char *s);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int fmtrunestrcpy(Fmt *f, Rune *s);
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int errfmt(Fmt *f);<br>
</font></tt>
</table>
<p><font size=+1><b>DESCRIPTION </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
The interface described here allows the construction of custom
<a href="../man3/print.html"><i>print</i>(3)</a> verbs and output routines. In essence, they provide access
to the workings of the formatted print code.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
The <a href="../man3/print.html"><i>print</i>(3)</a> suite maintains its state with a data structure called
<tt><font size=+1>Fmt</font></tt>. A typical call to <a href="../man3/print.html"><i>print</i>(3)</a> or its relatives initializes a
<tt><font size=+1>Fmt</font></tt> structure, passes it to subsidiary routines to process the
output, and finishes by emitting any saved state recorded in the
<tt><font size=+1>Fmt</font></tt>. The details of the <tt><font size=+1>Fmt</font></tt> are unimportant to outside users,
except
insofar as the general design influences the interface. The <tt><font size=+1>Fmt</font></tt>
records whether the output is in runes or bytes, the verb being
processed, its precision and width, and buffering parameters.
Most important, it also records a <i>flush</i> routine that the library
will call if a buffer overflows. When printing to a file descriptor,
the
flush routine will emit saved characters and reset the buffer;
when printing to an allocated string, it will resize the string
to receive more output. The flush routine is nil when printing
to fixed-size buffers. User code need never provide a flush routine;
this is done internally by the library.<br>
<p><font size=+1><b>Custom output routines </b></font><br>
To write a custom output routine, such as an error handler that
formats and prints custom error messages, the output sequence
can be run from outside the library using the routines described
here. There are two main cases: output to an open file descriptor
and output to a string.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
To write to a file descriptor, call <i>fmtfdinit</i> to initialize the
local <tt><font size=+1>Fmt</font></tt> structure <i>f</i>, giving the file descriptor <i>fd</i>, the buffer
<i>buf</i>, and its size <i>nbuf</i>. Then call <i>fmtprint</i> or <i>fmtvprint</i> to generate
the output. These behave like <tt><font size=+1>fprint</font></tt> (see <a href="../man3/print.html"><i>print</i>(3)</a>) or <tt><font size=+1>vfprint</font></tt>
except that the characters are buffered until <i>fmtfdflush</i> is called
and the return value is either 0 or –1. A typical example of this
sequence appears in the Examples section.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
The same basic sequence applies when outputting to an allocated
string: call <i>fmtstrinit</i> to initialize the <tt><font size=+1>Fmt</font></tt>, then call <i>fmtprint</i>
and <i>fmtvprint</i> to generate the output. Finally, <i>fmtstrflush</i> will
return the allocated string, which should be freed after use.
To output to a rune string, use <i>runefmtstrinit</i> and <i>runefmtstrflush</i>.
Regardless of the output style or type, <i>fmtprint</i> or <i>fmtvprint</i>
generates the characters.<br>
<p><font size=+1><b>Custom format verbs </b></font><br>
<i>Fmtinstall</i> is used to install custom verbs and flags labeled by
character <i>c</i>, which may be any non-zero Unicode character. <i>Fn</i> should
be declared as<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>int fn(Fmt*)<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
</table>
<i>Fp</i><tt><font size=+1>−>r</font></tt> is the flag or verb character to cause <i>fn</i> to be called. In
<i>fn</i>, <i>fp</i><tt><font size=+1>−>width</font></tt><i>, fp</i><tt><font size=+1>−>prec</font></tt> are the width and precision, and <i>fp</i><tt><font size=+1>−>flags</font></tt>
the decoded flags for the verb (see <a href="../man3/print.html"><i>print</i>(3)</a> for a description
of these items). The standard flag values are: <tt><font size=+1>FmtSign</font></tt> (<tt><font size=+1>+</font></tt>), <tt><font size=+1>FmtLeft</font></tt>
(<tt><font size=+1>−</font></tt>), <tt><font size=+1>FmtSpace</font></tt> (<tt><font size=+1>' '</font></tt>), <tt><font size=+1>FmtSharp</font></tt> (<tt><font size=+1>#</font></tt>),
<tt><font size=+1>FmtComma</font></tt> (<tt><font size=+1>,</font></tt>), <tt><font size=+1>FmtLong</font></tt> (<tt><font size=+1>l</font></tt>), <tt><font size=+1>FmtShort</font></tt> (<tt><font size=+1>h</font></tt>), <tt><font size=+1>FmtUnsigned</font></tt> (<tt><font size=+1>u</font></tt>), and
<tt><font size=+1>FmtVLong</font></tt> (<tt><font size=+1>ll</font></tt>). The flag bits <tt><font size=+1>FmtWidth</font></tt> and <tt><font size=+1>FmtPrec</font></tt> identify whether
a width and precision were specified.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Fn</i> is passed a pointer to the <tt><font size=+1>Fmt</font></tt> structure recording the state
of the output. If <i>fp</i><tt><font size=+1>−>r</font></tt> is a verb (rather than a flag), <i>fn</i> should
use <tt><font size=+1>Fmt−>args</font></tt> to fetch its argument from the list, then format
it, and return zero. If <i>fp</i><tt><font size=+1>−>r</font></tt> is a flag, <i>fn</i> should return one.
All interpretation of <i>fp</i><tt><font size=+1>−>width</font></tt>, <i>fp</i><tt><font size=+1>−>prec</font></tt>, and <i>fp-></i><tt><font size=+1>flags</font></tt> is
left up to the conversion routine. <i>Fmtinstall</i> returns 0 if the
installation succeeds, –1 if it fails.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Fmtprint</i> and <i>fmtvprint</i> may be called to help prepare output in
custom conversion routines. However, these functions clear the
width, precision, and flags. Both functions return 0 for success
and –1 for failure.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
The functions <i>dofmt</i> and <i>dorfmt</i> are the underlying formatters;
they use the existing contents of <tt><font size=+1>Fmt</font></tt> and should be called only
by sophisticated conversion routines. These routines return the
number of characters (bytes of UTF or runes) produced.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
Some internal functions may be useful to format primitive types.
They honor the width, precision and flags as described in <a href="../man3/print.html"><i>print</i>(3)</a>.
<i>Fmtrune</i> formats a single character <tt><font size=+1>r</font></tt>. <i>Fmtstrcpy</i> formats a string
<tt><font size=+1>s</font></tt>; <i>fmtrunestrcpy</i> formats a rune string <tt><font size=+1>s</font></tt>. <i>Errfmt</i> formats the system
error string. All these routines return zero for
successful execution. Conversion routines that call these functions
will work properly regardless of whether the output is bytes or
runes.<br>
</table>
<p><font size=+1><b>EXAMPLES </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
This function prints an error message with a variable number of
arguments and then quits. Compared to the corresponding example
in <a href="../man3/print.html"><i>print</i>(3)</a>, this version uses a smaller buffer, will never truncate
the output message, but might generate multiple <tt><font size=+1>write</font></tt> system calls
to produce its output.
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>#pragma varargck argpos error 1<br>
void fatal(char *fmt, ...)<br>
{<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Fmt f;<br>
char buf[64];<br>
va_list arg;<br>
fmtfdinit(&f, 1, buf, sizeof buf);<br>
fmtprint(&f, "fatal: ");<br>
va_start(arg, fmt);<br>
fmtvprint(&f, fmt, arg);<br>
va_end(arg);<br>
fmtprint(&f, "\n");<br>
fmtfdflush(&f);<br>
exits("fatal error");<br>
</table>
}<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
</table>
This example adds a verb to print complex numbers.<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>typedef<br>
struct {<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
double r, i;<br>
</table>
} Complex;<br>
#pragma varargck type "X" Complex<br>
int<br>
Xfmt(Fmt *f)<br>
{<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Complex c;<br>
c = va_arg(f−>args, Complex);<br>
return fmtprint(f, "(%g,%g)", c.r, c.i);<br>
</table>
}<br>
main(...)<br>
{<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
Complex x = (Complex){ 1.5, −2.3 };<br>
fmtinstall('X', Xfmt);<br>
print("x = %X\n", x);<br>
</table>
}<br>
</font></tt>
</table>
</table>
<p><font size=+1><b>SOURCE </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>/usr/local/plan9/src/lib9/fmt<br>
</font></tt>
</table>
<p><font size=+1><b>SEE ALSO </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<a href="../man3/print.html"><i>print</i>(3)</a>, <a href="../man7/utf.html"><i>utf</i>(7)</a>, <a href="../man3/errstr.html"><i>errstr</i>(3)</a><br>
</table>
<p><font size=+1><b>DIAGNOSTICS </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
These routines return negative numbers or nil for errors and set
<i>errstr</i>.<br>
</table>
<td width=20>
<tr height=20><td>
</table>
<!-- TRAILER -->
<table border=0 cellpadding=0 cellspacing=0 width=100%>
<tr height=15><td width=10><td><td width=10>
<tr><td><td>
<center>
<a href="../../"><img src="../../dist/spaceglenda100.png" alt="Space Glenda" border=1></a>
</center>
</table>
<!-- TRAILER -->
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