system_data_types.7: Add 'intptr_t'

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/system_data_types.7

@@ -468,6 +468,71 @@ and
 .I unsigned __int128
 types in this page.
 .RE
+.\"------------------------------------- intptr_t ---------------------/
+.TP
+.I intptr_t
+.RS
+Include:
+.IR <stdint.h> .
+Alternatively,
+.IR <inttypes.h> .
+.PP
+A signed integer type
+such that any valid
+.RI ( "void *" )
+value can be converted to this type and back.
+According to the C language standard, it shall be
+capable of storing values in the range
+.RB [ INTPTR_MIN ,
+.BR INTPTR_MAX ].
+.PP
+The length modifier for
+.I intptr_t
+for the
+.BR printf (3)
+family of functions
+is expanded by the macros
+.B PRIdPTR
+and
+.B PRIiPTR
+(defined in
+.IR <inttypes.h> );
+resulting commonly in
+.B %"PRIdPTR"
+or
+.B %"PRIiPTR"
+for printing
+.I intptr_t
+values.
+The length modifier for
+.I intptr_t
+for the
+.BR scanf (3)
+family of functions
+is expanded by the macros
+.B SCNdPTR
+and
+.B SCNiPTR,
+(defined in
+.IR <inttypes.h> );
+resulting commonly in
+.B %"SCNdPTR"
+or
+.B %"SCNiPTR"
+for scanning
+.I intptr_t
+values.
+.PP
+Conforming to:
+C99 and later; POSIX.1-2001 and later.
+.PP
+See also the
+.I uintptr_t
+and
+.I void *
+.\" TODO: Document void *
+types in this page.
+.RE
 .\"------------------------------------- lconv ------------------------/
 .TP
 .I lconv