Chapter 8

Setting Values

Given an initialized SV, you can load it with any of the value types using the sv_set*

family of functions:

sv_setiv(sv,  10);   // sv contains the signed integer (IV)  10

sv_setuv(sv, 10);    // sv contains the unsigned integer (UV) 10

sv_setnv(sv, 10.5);  // sv contains the unsigned integer (UV)  10

sv_setpv(sv, "10");  // sv contains the string value (PV) "10"

The PV forms also come in a few more flavors. There's one that uses an 

sprintf() style format string:

sv_setpvf(sv, "ten: %d", 10);  // sv contains the string value (PV) "ten: 10"

and one that takes a length argument to allow for strings that aren't null termi 

nated or that contain null bytes:

sv_setpvn(sv, "10", 2);  // sets sv to the 2 character string "10"

Direct Access

If you know the type of an SV, then you can directly access the underlying value 

type using the an Sv*X macro. This is useful for two reasons it is faster since it 

avoids testing the type of the data, and it is lvaluable. In C, a macro is said to be 

lvaluable if it may legally be used as an lvalue. The most common lvalue is the left 

hand side of an assignment operator. Sv*X allows you to efficiently set the value of 

an SV without needing to call a function.

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

SvUVX(sv_uv) = 100;           // directly set the UV inside sv_uv to 100

SvNVX(sv_nv) = 100.10;        // directly set the NV inside sv_nv to 100.5

warn("PV: %s", SvPVX(sv_pv)); // directly access the string inside sv_pv

Note that you cannot safely use the return value from SvPVX() as an lvalue 

doing so would change the string pointed to by the SV and would cause an instant 

memory leak. Other bad things would happen too, because the SV structure keeps 

track of more than just the pointer to the string it also tracks the length and an 

offset into the string buffer where the string begins.

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