Programming Perl in C

There are also tests that combine one or more of the preceding tests:

if (SvNIOK(sv))      warn("sv contains a number of some type (IV, UV or NV)");

if (SvIOK(sv))       warn("sv contains an integer of some type (IV or UV)");

Getting Values

The following macros return the value stored inside the SV as the requested type. If 

necessary, they will convert the value to the requested type.

IV iv = SvIV(sv);          // get an IV from sv

UV uv = SvUV(sv);          // get a UV from sv

NV nv = SvNV(sv);          // get an NV from sv

STRLEN len;

char  *pv = SvPV(sv, len); // get a PV from sv, setting len to the

                           // length of the string

NOTE If an SV contains a nonnumeric string, then calling SvIV(),

SvUV(), or SvNV() on it will result in the value 0. To find out if an SV

contains something that will result in a valid number, use the 

looks_like_number() function.

These functions can have a side effect they may change the internal repre 

sentation of the SV. For example, after a call to SvPV(), the stringified form of the SV

will be cached inside the SV, and both SvIOK and SvPOK will return true. As a result, 

future calls to SvPV on this scalar will use the cached copy instead of doing the con 

version again. This has two implications: First, the type of an SV may change even 

if it isn't written to, and second, the memory usage of an SV may grow even if it isn't 

written to.

There is a version of SvPV that is guaranteed to produce an SV with only a string 

value, SvPV_force. The behavior is the same as SvPV, but afterward only SvPOK will 

return true and only the string value will be retained inside the SV. This function is 

necessary if you're going to be changing the string value directly with the SvPVX

macro introduced later.

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