fmt.h File Reference

libc-free printf-compatible formatter. More...

#include "common/bytes/span/span.h"
#include "common/platform/sys/syscall.h"

Go to the source code of this file.

Macros
#define	wired_va_start(ap, last)
	Begin reading variadic arguments after last.
#define	wired_va_arg(ap, type)
	Fetch the next variadic argument as type.
#define	wired_va_end(ap)
	End variadic argument reading.

Typedefs
typedef __builtin_va_list	wired_va_list
	Variadic argument list (compiler builtin, not ISA specific).

Functions
usz	wired_vsnprintf (char *out, usz cap, const char *fmt, wired_va_list ap)
	Format into out like C99 vsnprintf.
usz	wired_snprintf (char *out, usz cap, const char *fmt,...)
	Format into out like C99 snprintf; see wired_vsnprintf.
usz	wired_obuf_printf (wired_obuf *b, const char *fmt,...)
	Append formatted text to b at b->len, like snprintf into the free space.
ssz	wired_dprintf (i64 fd, const char *fmt,...)
	Format and write to a file descriptor via write(2).

Detailed Description

libc-free printf-compatible formatter.

Conversions: d i u x X p s c %% f; length modifiers hh h l ll z; flags - 0 + space #; width, precision, and * for both.

Deviations from C99 (deliberate, to stay small):

• p prints "0x" + lowercase hex, and NULL prints "0x0".
• s with a NULL pointer prints "(null)" regardless of precision.
• f rounds half-to-even on the exact binary value (as glibc does). Magnitudes at or above 2^64 saturate the integer part to 18446744073709551615; precision above 40 is clamped to 40; the fraction is exact to 2^-60.
• An unknown conversion is copied through verbatim ("%" + the char).

Macro Definition Documentation

wired_va_arg

#define wired_va_arg	(		ap,
			type )

Value:

__builtin_va_arg(ap, type)

Fetch the next variadic argument as type.

wired_va_end

#define wired_va_end

(

ap

)

Value:

__builtin_va_end(ap)

End variadic argument reading.

wired_va_start

#define wired_va_start	(		ap,
			last )

Value:

__builtin_va_start(ap, last)

Begin reading variadic arguments after last.

Function Documentation

wired_dprintf()

ssz wired_dprintf	(	i64	fd,
		const char *	fmt,
			... )

Format and write to a file descriptor via write(2).

The output is formatted into a 512-byte buffer, so anything beyond 511 bytes is truncated; short writes are retried.

Parameters

fd	file descriptor
fmt	printf format string

Returns

bytes written, or the negative error from write(2)

wired_obuf_printf()

usz wired_obuf_printf	(	wired_obuf *	b,
		const char *	fmt,
			... )

Append formatted text to b at b->len, like snprintf into the free space.

At most cap - len - 1 bytes are appended (vsnprintf's NUL needs the last byte; it is not counted in len), so output that does not fit is cut.

Parameters

b	buffer to append to (e.g. an HTTP response body)
fmt	printf format string

Returns

bytes appended (b->len advanced by the same amount)

wired_snprintf()

usz wired_snprintf	(	char *	out,
		usz	cap,
		const char *	fmt,
			... )

Format into out like C99 snprintf; see wired_vsnprintf.

Parameters

out	destination
cap	capacity of out in bytes, including the NUL
fmt	printf format string

Returns

the would-be length, excluding the NUL

wired_vsnprintf()

usz wired_vsnprintf	(	char *	out,
		usz	cap,
		const char *	fmt,
		wired_va_list	ap )

Format into out like C99 vsnprintf.

Parameters

out	destination (may be NULL when cap is 0)
cap	capacity of out in bytes, including the NUL
fmt	printf format string
ap	arguments

Returns

the length the full output would have (excluding the NUL); output is truncated and NUL-terminated when this is >= cap