try lowercase hex string, it must help

_This answer was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Newton

Hey this message looks very confusing.
`GatewayError: {'contract_address': ['Expected hex string, got: "0x01C438231cD70f47d1acB8404E51734c1Fb4d79AC55813b3E861fB1EF78Da0D6".']}`

Any hints on this?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

CairoLang error: `GatewayError: {'contract_address': ['Expected hex string, got: 


I am going through the official [Cairo language tutorial](https://www.cairo-lang.org/docs/hello_cairo/dict.html). When I get to the `build_dict` function for the 15-puzzle, I am a bit confused so would like to print out some things to see.



```
struct Location:
    member row : felt
    member col : felt
end

...

func finalize_state(dict : DictAccess*, idx) -> (
        dict : DictAccess*):
    if idx == 0:
        return (dict=dict)
    end

    assert dict.key = idx
    assert dict.prev_value = idx - 1
    assert dict.new_value = idx - 1

    return finalize_state(
        dict=dict + DictAccess.SIZE, idx=idx - 1)
end

##### I added the {} along with context in it for output #####
func main{output_ptr : felt*}():
    alloc_locals

    local loc_tuple : (Location, Location, Location, Location, Location) = (
        Location(row=0, col=2),
        Location(row=1, col=2),
        Location(row=1, col=3),
        Location(row=2, col=3),
        Location(row=3, col=3),
        )

    # Get the value of the frame pointer register (fp) so that
    # we can use the address of loc_tuple.
    let (__fp__, _) = get_fp_and_pc()
    # Since the tuple elements are next to each other we can use the
    # address of loc_tuple as a pointer to the 5 locations.
    verify_location_list(
        loc_list=cast(&loc_tuple, Location*), n_steps=4)

    ##### Here is what I added #####
    local locs : Location* = cast(&loc_tuple, Location*)
    tempvar loc = [locs]
    tempvar row = loc.row
    serialize_word(row)
    ################################

    return ()
end

```

I added the lines for printing the first row in `loc_tuple`. However, the Cairo compiler is giving me the following errors:



```
Traceback (most recent call last):
  File "/Users/yijiachen/cairo_venv/bin/cairo-compile", line 10, in <module>
    sys.exit(main())
  File "/Users/yijiachen/cairo_venv/lib/python3.8/site-packages/starkware/cairo/lang/compiler/cairo_compile.py", line 397, in main
    cairo_compile_common(
  File "/Users/yijiachen/cairo_venv/lib/python3.8/site-packages/starkware/cairo/lang/compiler/cairo_compile.py", line 121, in cairo_compile_common
    assembled_program = assemble_func(
  File "/Users/yijiachen/cairo_venv/lib/python3.8/site-packages/starkware/cairo/lang/compiler/cairo_compile.py", line 367, in 
    cairo_assemble_program
    check_main_args(program)
  File "/Users/yijiachen/cairo_venv/lib/python3.8/site-packages/starkware/cairo/lang/compiler/cairo_compile.py", line 296, in check_main_args
    assert main_args == expected_builtin_ptrs, (
AssertionError: Expected main to contain the following arguments (in this order): []. Found: ['output_ptr'].

```

I have tried with various `serialize_word` statements and none seem to work. This issue never arose before with other `serialize_word` statements, including in earlier parts of the tutorial.



ㅤ
_This question was originally posted on [Stack Overflow](https://stackoverflow.com/questions/70586553/output-ptr-assertion-error-in-main-cairo-lang)_

output_ptr Assertion Error in Main - Cairo-lang

How do I interact with my Pathfinder node?

Is there a way besides manually checking the address in every function to make a function contract owner only


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/222)_

Cairo Owner Only Fuctions

Hi people. I can't seem to be able to update to 0.3.3.

I am using docker, and when and successfully pull with

*docker pull eqlabs/pathfinder*

but then

*docker run \
  --rm \
  -p 9545:9545 \
  --user "$(id -u):$(id -g)" \
  -e RUST_LOG=info \
  -e PATHFINDER_ETHEREUM_API_URL="https://goerli.infura.io/v3/<project-id>" \
  -v $HOME/pathfinder:/usr/share/pathfinder/data \
  eqlabs/pathfinder*

makes the node run with 0.3.0-alpha

Anyone encountering the same issue ?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

An issue while updating to 0.3.3 node StarkNet

Hello, I am getting the following error in my starknet contract, does anyone know how to resolve it?


`Accessing struct/tuple members for r-value structs is not supported yet.`


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/665)_

Cairo error: Accessing struct/tuple members for r-value structs is not supported yet

Hello everyone. Does anyone happen to know if there's a way to get the block hash in cario? I found out about `get_block_number` and `get_block_timestamp`, but is there something similar for block hash?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

How to get the block hash in Cairo lang?

Hey,
As each storage value is by default initialized to 0, does writing it to zero actually do something? Does it use storage in layer 1 with value 0? Or does it just do nothing?
Should I check that the value I want to write is different than 0 before writing it otherwise I will waste storage?

The same idea: does writing a storage value to 0 free storage on l1

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CairoLang error: `GatewayError: {'contract_address': ['Expected hex string, got:

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