How to get keys from hash - ruby c extension

Question

I am looking for a function which can get me all the keys from hash or I can loop through the hash to retrieve single key at a time.

Currently I am hardcoding key

VALUE option = rb_hash_aref(options, rb_str_new2("some_key"));

Brittaniebrittany

Answer 1

You can iterate over the key/value pairs with a callback function using rb_hash_foreach (blog post w/an example):

void rb_hash_foreach(VALUE, int (*)(ANYARGS), VALUE);

There is an rb_hash_keys in MRI, but it's not in any header files it seems, so using it may be risky.

Allanallana

Yup rb_hash_keys complains use of undeclared identifier 'rb_hash_keys' – Brittaniebrittany

Do you have any working example? I am getting this error candidate function not viable: no known conversion from 'int (VALUE, VALUE, VALUE)' to 'int (*)(...)' for 2nd argument void rb_hash_foreach(VALUE, int (*)(ANYARGS), VALUE); – Brittaniebrittany

The MRI source has an example in rb_hash_keys: rxr.whitequark.org/mri/source/hash.c#1627 – Allanallana

error: use of undeclared identifier 'rb_hash_keys'; – Brittaniebrittany

Well yeah, that function contains the example. – Allanallana

I followed MRI source example but eventually I got the same error candidate function not viable: no known conversion from 'int (VALUE, VALUE, VALUE)' to 'int (*)(...)' for 2nd argument void rb_hash_foreach(VALUE, int (*)(ANYARGS), VALUE);This is the code I am trying ` VALUE ary; ary = rb_ary_new(); rb_hash_foreach(opts, convert_keys_to_a, ary);` static int convert_keys_to_a(VALUE key, VALUE value, VALUE ary) { if (logic) return ST_CONTINUE; if (logic { rb_hash_foreach(value, convert_keys_to_a, ary); } return rb_ary_push(ary, key); } – Brittaniebrittany

What ruby version? Compiler? Compiler flags? How are you building this? Empty functions with these names compiles fine for me using these basic instructions. – Allanallana

If you are compiling for Rubinius, you may need to include the hash libraries yourself (they are not automatically included with ruby.h): // Force inclusion of hash declarations (only MRI includes by default) #ifdef HAVE_RUBY_ST_H #include "ruby/st.h" #else #include "st.h" #endif – Wirth

Answer 2

You could always make a call to the Ruby method itself:

VALUE keys = rb_funcall(hash, rb_intern("keys"), 0)

Brittne