Programming Perl in C

CAUTION Be careful with Sv*X macros; if you use one without first 

checking that the SV is of the correct type, you might get a segmentation 

fault, or worse, silently corrupt nearby data in memory!

After using an Sv*X macro to update the value inside an SV, it's often necessary 

to update the type information of the SV. This is because SVs will cache conversion 

values when converting between types. You need to tell the SV to invalidate any 

other cached representations using a macro of the form Sv*OK_only(). For example:

SvIVX(sv_iv) = 100;    // directly set the IV inside sv_iv to 100

SvIOK_only(sv_iv);     // invalidate non IV representations inside sv_iv

In general it is better to use the sv_set functions rather than Sv*X macros. 

However, in some cases the performance improvement can make it worth the risk.

String Functions

Just like Perl, the Perl API contains functionality to make string processing easier. 

There are a set of functions for string concatenation:

sv_catpv(sv, "foo");          // adds "foo" to the end of sv

sv_catpvn(sv, "foo", 3);      // adds "foo" to the end of sv, with a length arg

sv_catpvf(sv, "ten: %d", 10); // adds "ten: 10" to the end of sv

sv_catsv(sv_to, sv_from);     // adds the contents of sv_from to the

                              // end of sv_to

Getting the length of an SV is done as follows:

STRLEN len = sv_len(sv);

If you want to grow the size of the string, do the following:

char *new_ptr = sv_grow(sv, 1024); // grows sv to 1k and returns a pointer to

                                   // the new character buffer

Truncate the string in this manner:

SvCUR_set(sv, 10);                 // the SV is now 10 bytes long

Inserting a string into the middle of an SV, similar to the substr built in in Perl, 

is done as follows:

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