wprintf(“%s”,…)

By chys on June 28th, 2009

Microsoft and GNU interprets %s differently in the wide-string version of the printf-family functions (wprintf, etc.)

Microsoft: “when used with wprintf functions, specifies a wide-character string.”

C99 and GNU: “If no l modifier is present: The const char * argument is expected to be a pointer to an array of character type (pointer to a string).”

Fortunately, both accept “%ls” for wide strings.

Unfortunately, the only supported format specifier for multi-byte (narrow) strings in C99 is “%s”, which Microsoft interpret differently.

Fortunately, the specifier that Microsoft recommends for multi-byte strings, “%hs”, is also accepted by many other C libraries, though undocumented. ~~Such acceptance is very reasonable – the unknown prefix h is simply ignored. (I tested it with GNU and Solaris C libraries.)~~It seems such acceptance is necessary in order to strictly conform to the wording of C99.

	Microsoft `wprintf`	GNU `wprintf`	C99
`%s`	Wide	Narrow	Narrow
`%S`	Narrow	Wide (deprecated)
`%hs`	Narrow	Narrow (undocumented)
`%ls`	Wide	Wide	Wide

To draw a conclusion:

Everybody agrees that, in wprintf, “%ls” specifies a wide string. (I’m not sure whether VC6 supports it.)
There is no consensus on the specifier for multi-byte strings. The best practical choice is “%hs”.

This table and conclusion also apply to the “%c” family.