Octave - 访问八度值列表中的值

Question

I am working within a C++ development environment while using the Octave C++ API.

I would like to know how to access single values in a returned octave_value_list when calling functions.

For example when I am calling the clock-function im getting returned an octave_value_list which shows the following:

2014.0000 8.0000 22.0000 10.0000 1.0000 44.7120

I now would like to access each single value but Im somehow only able to get the year. I am missing some syntax, maybe someone can help me.

Answer 1

Useful documentation to answer your question:

• doxygen for octave_value_list
• doxygen for octave_value

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The values you mention are a multiple octave_value s in an octave_value_list , or is it a an array of values in a single octave_value in an octave_value_list ?

Note that a single octave_value is not necessarily a scalar value. It can be a an array with n dimensions, and multiple elements. It can be a struct, a struct array, or a cell array. It basically can be anything that an octave variable can be. For example, the call:

foo ([1 2 3], "string", {678, "other string"}, struct ("over", 9000))

will create an octave_value_list with 4 octave_value s and:

foo ([1 2 3])

will still create an octave_value_list but with a single octave_value .

The first thing you need is to figure out what you actually have. You can use octave_value_list.length() to get an idea and you can get individual octave_value s by simply indexing them with round brackets () .

for (int i =0; i < list.length (); i++)
    do_stuff_with (list(i));

Once you get an octave_value you can try to convert into many things.

std::string   s  = val.string_value ();
bool          b  = val.bool_value ();
boolMatrix    bm = val.bool_matrix_value ();
Cell          c  = val.cell_value ();
NDarray       nd = val.array_value ();
int           i  = val.int_value ();
Array<double> ad = val.vector_value ();

While you can use one of the is_x() methods of octave_value , the recommendation is to check the value of error_state after a conversion to check if anything went wrong. This will give a more natural Octave experience and will handle conversion between different types that you'd expect in Octave for you.