vsnprintf (9)

int vsnprintf(char * buf, size_t size, const char * fmt, va_list args);

buf

The buffer to place the result into

size

The size of the buffer, including the trailing null space

fmt

The format string to use

args

Arguments for the format string

This function follows C99 vsnprintf, but has some extensions: pS output the name of a text symbol with offset ps output the name of a text symbol without offset pF output the name of a function pointer with its offset pf output the name of a function pointer without its offset pB output the name of a backtrace symbol with its offset pR output the address range in a struct resource with decoded flags pr output the address range in a struct resource with raw flags pM output a 6-byte MAC address with colons pMR output a 6-byte MAC address with colons in reversed order pMF output a 6-byte MAC address with dashes pm output a 6-byte MAC address without colons pmR output a 6-byte MAC address without colons in reversed order pI4 print an IPv4 address without leading zeros pi4 print an IPv4 address with leading zeros pI6 print an IPv6 address with colons pi6 print an IPv6 address without colons pI6c print an IPv6 address as specified by RFC 5952 pIS depending on sa_family of 'struct sockaddr *' print IPv4/IPv6 address piS depending on sa_family of 'struct sockaddr *' print IPv4/IPv6 address pU[bBlL] print a UUID/GUID in big or little endian using lower or upper case. %*ph[CDN] a variable-length hex string with a separator (supports up to 64 bytes of the input) n is ignored

** Please update Documentation/printk-formats.txt when making changes **

The return value is the number of characters which would be generated for the given input, excluding the trailing '\0', as per ISO C99. If you want to have the exact number of characters written into buf as return value (not including the trailing '\0'), use vscnprintf. If the return is greater than or equal to size, the resulting string is truncated.

If you're not already dealing with a va_list consider using snprintf.