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man pages section 9: DDI and DKI Kernel Functions

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Updated: Thursday, June 13, 2019



vsprintf - format characters in memory


#include <sys/varargs.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>

char *vsprintf(char *buf, const char *fmt, va_list ap);

Interface Level

Solaris DDI specific (Solaris DDI).



Pointer to a character string.


Pointer to a character string.


Pointer to a variable argument list.


vsprintf() builds a string in buf under the control of the format fmt. The format is a character string with either plain characters, which are simply copied into buf, or conversion specifications, each of which converts zero or more arguments, again copied into buf. The results are unpredictable if there are insufficient arguments for the format; excess arguments are simply ignored. It is the user's responsibility to ensure that enough storage is available for buf.

ap contains the list of arguments used by the conversion specifications in fmt. ap is a variable argument list and must be initialized by calling va_start(9F). va_end(9F) is used to clean up and must be called after each traversal of the list. Multiple traversals of the argument list, each bracketed by va_start(9F) and va_end(9F), are possible.

Each conversion specification is introduced by the % character, after which the following appear in sequence:

An optional decimal digit specifying a minimum field width for numeric conversion. The converted value will be right-justified and padded with leading zeroes if it has fewer characters than the minimum.

An optional l (ll) specifying that a following d, D, o , O, x, X, or u conversion character applies to a long (long long) integer argument. An l (ll) before any other conversion character is ignored.

A character indicating the type of conversion to be applied:

d, D,o,O,x, X,u

The integer argument is converted to signed decimal (d, D), unsigned octal (o, O), unsigned hexadecimal (x, X) or unsigned decimal ( u), respectively, and copied. The letters abcdef are used for x conversion. The letters ABCDEF are used for X conversion.


The character value of the argument is copied.


This conversion uses two additional arguments. The first is an integer, and is converted according to the base specified in the second argument. The second argument is a character string in the form <base >[<arg > . . . ]. The base supplies the conversion base for the first argument as a binary value; \10 gives octal, \20 gives hexadecimal. Each subsequent <arg> is a sequence of characters, the first of which is the bit number to be tested, and subsequent characters, up to the next bit number or terminating null, supply the name of the bit.

A bit number is a binary-valued character in the range 1-32. For each bit set in the first argument, and named in the second argument, the bit names are copied, separated by commas, and bracketed by < and >. Thus, the following function call would generate reg=3<BitTwo,BitOne>\n in buf.

vsprintf(buf, "reg=%b\n", 3, "\10\2BitTwo\1BitOne")


The argument is taken to be a string (character pointer), and characters from the string are copied until a null character is encountered. If the character pointer is NULL on SPARC, the string <nullstring> is used in its place; on x86, it is undefined.


Copy a %; no argument is converted.

Return Values

vsprintf() returns its first parameter, buf.


vsprintf() can be called from user, kernel, or interrupt context.


Example 1 Using vsprintf()

In this example, xxerror() accepts a pointer to a dev_info_t structure dip, an error level level, a format fmt, and a variable number of arguments. The routine uses vsprintf() to format the error message in buf. Note that va_start(9F) and va_end(9F) bracket the call to vsprintf(). instance, level, name, and buf are then passed to cmn_err(9F).

#include <sys/varargs.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
#define MAX_MSG 256

xxerror(dev_info_t *dip, int level, const char *fmt, . . . )
	va_list		ap;
	int		instance;
	char		buf[MAX_MSG],

	instance = ddi_get_instance(dip);
	name = ddi_binding_name(dip);

	/* format buf using fmt and arguments contained in ap */
	va_start(ap, fmt);
	vsprintf(buf, fmt, ap); 	

	/* pass formatted string to cmn_err(9F) */
	cmn_err(level, "%s%d: %s", name, instance, buf);

See Also

va_arg(9F), cmn_err(9F), ddi_binding_name(9F), ddi_get_instance(9F)

Writing Device Drivers in Oracle Solaris 11.4