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Section: 17.2 [support.types] Status: NAD Submitter: Matt Austern Opened: 2013-04-19 Last modified: 2016-01-28
Priority: 3
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Discussion:
The C++ standard library defines size_t, a typedef for an implementation defined unsigned integer type that can represent the sizes of objects. The POSIX standard augments this with ssize_t, a typedef for a signed integer type that corresponds to size_t.
The ssize_t typedef is useful — useful enough that the C++ standard even refers to it. (In a non-normative footnote in 31.2.2 [stream.types].) Also, lots of OS vendors add it to their headers anyway, even though it isn't part of the C or C++ standards, because those vendors are trying to define headers that conform to multiple standards at once. We should make users' and implementers' lives easier by adding ssize_t to 17.2 [support.types].[2013-09-29, Suggested wording from Jayson Oldfather]
I decided to use the phrase to describe ssize_t below because of the text describing it in the POSIX standard. In it, it describes ssize_t with the value range of [-1,{SSIZE_MAX}]. SSIZE_MAX is specified in the POSIX standard as a minimum value of _POSIX_SSIZE_MAX. This macro is referenced in the wording below.
[Lenexa 2015-05-05: NAD - no consensus for a change]
Billy : ssize_t that was promised to be signed, was based on rsize_t from safe secure C
NM : ssize_t s ptrdif_t
Z : ptrdiff_t is full range, ssize_t has only -1 as negative value
Billy : motivations for ptrdiff_T, ssize_t and rsize_T all fuzzy. - Reads rsize max -
NM : ptrdiff_T not big enough to rep difference of pointers anymore
STL : description incorporates posixisms
Billy : Don't need it
NM : rather remove it from footnote
Z : Name has precise meaning
STL : everyone understands ptrdiff_t is signed counterpart to size_t
Billy : Not in all implementations anymore
DK : footnote says something different from ...
Z/NM : off_t historically tainted
STL : we have a type trait to make signed version of size_t. we should just use that
MC : NAD; is feature request
TP : It's not cstdsef
Proposed resolution:
Ammend 17.2 [support.types], Table 30 as indicated:
Table 30 — Header <cstddef> synopsis Type Name(s) Macros: NULL offset_t Types: ptrdiff_t ssize_t size_t max_align_t nullptr_t
Add the following paragraph to describe ssize_t
-?- The type ssize_t is an implementation-defined signed integer type that shall contain the minimum range [-1, {SSIZE_MAX}] where SSIZE_MAX is specified at a minimum of _POSIX_SSIZE_MAX.
Ammend p7 as follows:
-7- [Note: It is recommended that implementations choose types for ptrdiff_t, ssize_t, and size_t whose integer conversion ranks …