socklen_t (Re: Multicast problems [PATCH])

Harti Brandt hartmut.brandt at
Wed Jun 20 12:59:10 UTC 2007

On Wed, 20 Jun 2007, Daniel Eischen wrote:

DE>On Wed, 20 Jun 2007, Stefan Farfeleder wrote:
DE>> On Tue, Jun 19, 2007 at 06:36:39PM -0400, Daniel Eischen wrote:
DE>> >  POSIX states that:
DE>> > 
DE>> >    o The <sys/socket.h> header shall define the type socklen_t,
DE>> >      which is an integer type of width of at least 32 bits; see
DE>> > 
DE>> >  and goes on to state:
DE>> > 
DE>> >    o The <sys/socket.h> header shall define the unsigned integer
DE>> >      type sa_family_t.
DE>> > 
DE>> >  This seems to imply that our socklen_t should not be an unsigned
DE>> >  integer (uint32_t), but a signed integer.  In APPLICATION USAGE,
DE>> >  POSIX states:
DE>> I don't understand how you come to that conclusion.  Why does not
DE>> mentioning whether socklen_t is signed or unsigned imply it should be
DE>> signed?
DE>Because it explicitly says unsigned for sa_family_t and does not
DE>say unsigned for socklen_t.  To me, "integer" means a C (signed)
DE>integer.  The fact that older APIs and implementations used "int"
DE>might support the argument to use int32_t just for compatibility
DE>reasons.  As it stands now, portable code has to have some sort
DE>of autoconfig to determine whether or not to use socklen_t or int.
DE>I don't see how you can do this with #ifdefs unless you know
DE>OS version numbers and when socklen_t first got introduced.

In standardese stating 'integer type' means any integer type. It does not 
imply signed or unsignedness. You might look at paragraph 14 of 6.2.5 of 
the C standard: "The type char, the signed and unsigned integer types, and 
the enumerated types are collectively called integer types."

DE> DE>> >    To forestall portability problems, it is recommended that
DE>> >    applications not use values larger than 23^1 -1 for the
DE>> >    socklen_t type.
DE>> That just means that those values will wrap to negative values if
DE>> socklen_t is a signed integer type.

It ensures that the code works whether the type is signed or unsigned.


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