H All, I am having problems determining if a SV * points to a valid scalar. This example illustrates the problem: 
void
test()
    PREINIT:
        SV *scalar;
    CODE:
        if ( scalar == NULL ) // fixed
            std::cout << "NULL\n"
        if ( SvOK( scalar ) ) // fixed
            std::cout << "OK\n"

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This example prints "OK". The easy solution for this example is to manually set scalar = NULL but I cannot do this. My hope is to handle perl hash arguments by stuffing them into a map: 
void
test( ... )
    PREINIT:
        std::map< std::string, SV *> args;
    INIT:
        for ( int i = 1; i < items; i += 2 )
            args[ SvP_nolen( ST(i) ) ]
                = ST( i + 1 );
    CODE:
        std::cout << "The value of `foo' is "
                  << SvP_nolen( args["foo"] )
                  << "\n";

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In this example, if the foo argument was never given, the map will return the default value for a SV * which will point to nothing.

I need to be able to test if a SV * has never been set. I was hoping that SvOK would not only tell me if the scalar was defined but if such a scalar existed. I can't find anything in perlguts that satisfies this requirement.

Does anyone know how to test if a SV * points to a valid scalar, or to test if a SV * has never been set?

Thanks in advance.

In reply to XS/Guts and unset scalar pointers by narse

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