Perl also uses two special typedefs, I32 and I16, which will always be at
least 32-bits and 16-bits long, respectively. (Again, there are U32 and U16,
-as well.)
+as well.) They will usually be exactly 32 and 16 bits long, but on Crays
+they will both be 64 bits.
=head2 Working with SVs
-An SV can be created and loaded with one command. There are four types of
-values that can be loaded: an integer value (IV), a double (NV),
-a string (PV), and another scalar (SV).
+An SV can be created and loaded with one command. There are five types of
+values that can be loaded: an integer value (IV), an unsigned integer
+value (UV), a double (NV), a string (PV), and another scalar (SV).
-The six routines are:
+The seven routines are:
SV* newSViv(IV);
+ SV* newSVuv(UV);
SV* newSVnv(double);
SV* newSVpv(const char*, int);
SV* newSVpvn(const char*, int);
SV* newSVpvf(const char*, ...);
SV* newSVsv(SV*);
-To change the value of an *already-existing* SV, there are seven routines:
+If you require more complex initialisation you can create an empty SV with
+newSV(len). If C<len> is 0 an empty SV of type NULL is returned, else an
+SV of type PV is returned with len + 1 (for the NUL) bytes of storage
+allocated, accessible via SvPVX. In both cases the SV has value undef.
+
+ SV* newSV(0); /* no storage allocated */
+ SV* newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */
+
+To change the value of an *already-existing* SV, there are eight routines:
void sv_setiv(SV*, IV);
void sv_setuv(SV*, UV);
warning.
-=over
-
=item GV_ADDWARN
Issues the warning:
t PERL_MAGIC_taint vtbl_taint Taintedness
U PERL_MAGIC_uvar vtbl_uvar Available for use by extensions
v PERL_MAGIC_vec vtbl_vec vec() lvalue
+ V PERL_MAGIC_vstring (none) v-string scalars
+ w PERL_MAGIC_utf8 vtbl_utf8 UTF-8 length+offset cache
x PERL_MAGIC_substr vtbl_substr substr() lvalue
y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
variable / smart parameter
~ PERL_MAGIC_ext (none) Available for use by extensions
When an uppercase and lowercase letter both exist in the table, then the
-uppercase letter is used to represent some kind of composite type (a list
-or a hash), and the lowercase letter is used to represent an element of
-that composite type. Some internals code makes use of this case
-relationship.
+uppercase letter is typically used to represent some kind of composite type
+(a list or a hash), and the lowercase letter is used to represent an element
+of that composite type. Some internals code makes use of this case
+relationship. However, 'v' and 'V' (vec and v-string) are in no way related.
The C<PERL_MAGIC_ext> and C<PERL_MAGIC_uvar> magic types are defined
specifically for use by extensions and will not be used by perl itself.
sanctioned for use in extensions) begins like this:
void
- Perl_sv_setsv(pTHX_ SV* dsv, SV* ssv)
+ Perl_sv_setiv(pTHX_ SV* dsv, IV num)
C<pTHX_> is one of a number of macros (in perl.h) that hide the
details of the interpreter's context. THX stands for "thread", "this",
explicit arguments.
When a core function calls another, it must pass the context. This
-is normally hidden via macros. Consider C<sv_setsv>. It expands into
+is normally hidden via macros. Consider C<sv_setiv>. It expands into
something like this:
- ifdef PERL_IMPLICIT_CONTEXT
- define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b)
+ #ifdef PERL_IMPLICIT_CONTEXT
+ #define sv_setiv(a,b) Perl_sv_setiv(aTHX_ a, b)
/* can't do this for vararg functions, see below */
- else
- define sv_setsv Perl_sv_setsv
- endif
+ #else
+ #define sv_setiv Perl_sv_setiv
+ #endif
This works well, and means that XS authors can gleefully write:
- sv_setsv(foo, bar);
+ sv_setiv(foo, bar);
and still have it work under all the modes Perl could have been
compiled with.
and aTHX_ macros to call a function that will return the context.
Thus, something like:
- sv_setsv(asv, bsv);
+ sv_setiv(sv, num);
in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
in effect:
- Perl_sv_setsv(Perl_get_context(), asv, bsv);
+ Perl_sv_setiv(Perl_get_context(), sv, num);
or to this otherwise:
- Perl_sv_setsv(asv, bsv);
+ Perl_sv_setiv(sv, num);
You have to do nothing new in your extension to get this; since
the Perl library provides Perl_get_context(), it will all just
over. You're on your own about bounds checking, though, so don't use it
lightly.
-All bytes in a multi-byte UTF8 character will have the high bit set, so
-you can test if you need to do something special with this character
-like this:
+All bytes in a multi-byte UTF8 character will have the high bit set,
+so you can test if you need to do something special with this
+character like this (the UTF8_IS_INVARIANT() is a macro that tests
+whether the byte can be encoded as a single byte even in UTF-8):
- UV uv;
+ U8 *utf;
+ UV uv; /* Note: a UV, not a U8, not a char */
- if (utf & 0x80)
+ if (!UTF8_IS_INVARIANT(*utf))
/* Must treat this as UTF8 */
uv = utf8_to_uv(utf);
else
value of the character; the inverse function C<uv_to_utf8> is available
for putting a UV into UTF8:
- if (uv > 0x80)
+ if (!UTF8_IS_INVARIANT(uv))
/* Must treat this as UTF8 */
utf8 = uv_to_utf8(utf8, uv);
else
not it's dealing with UTF8 data, so that it can handle the string
appropriately.
+Since just passing an SV to an XS function and copying the data of
+the SV is not enough to copy the UTF8 flags, even less right is just
+passing a C<char *> to an XS function.
+
=head2 How do I convert a string to UTF8?
If you're mixing UTF8 and non-UTF8 strings, you might find it necessary
=item *
If a string is UTF8, B<always> use C<utf8_to_uv> to get at the value,
-unless C<!(*s & 0x80)> in which case you can use C<*s>.
+unless C<UTF8_IS_INVARIANT(*s)> in which case you can use C<*s>.
=item *
-When writing to a UTF8 string, B<always> use C<uv_to_utf8>, unless
-C<uv < 0x80> in which case you can use C<*s = uv>.
+When writing a character C<uv> to a UTF8 string, B<always> use
+C<uv_to_utf8>, unless C<UTF8_IS_INVARIANT(uv))> in which case
+you can use C<*s = uv>.
=item *
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