Example of decoding a string

[Jen]

Hello,

Does anyone know where I can find an example of decoding a string? My .proto file has two int_32 and a string like so:

syntax = "proto3";

message DigitiserConfig {
  int32 digitiser_block_size = 1;
  int32 max_us_timing_error = 2;
  string file_name_base = 3;
}

I am able to very simply decode the integers like so:

DigitiserConfig digitiserConfig = DigitiserConfig_init_zero;

pb_istream_t stream = pb_istream_from_buffer((uint8_t *)buffer, actual_size);

if (!pb_decode(&stream, DigitiserConfig_fields, &digitiserConfig)) {

printf("Decoding failed: %s\n", PB_GET_ERROR(&stream));

return FX_FILE_CORRUPT; // Return error if decoding fails

}

and then access them from the digitiserConfig struct.

But the file_name_base is a pb_callback_t and I just can't figure out what I'm meant to do with that.

In the API reference it says:
" For decoding strings and bytes fields, the length has already been decoded and the callback function is given a length-limited substream. You can therefore check the total length in stream->bytes_left and read the data using pb_read."

I'm sure it's really basic but I just can't figure it out or find anything on this. I hope someone can point me in the right direction.

Thanks,

Jen

[Petteri Aimonen]

Hi,

The easiest way is to specify the maximum size for the string.

Then nanopb will make a char[] array to store it.

See for example

https://github.com/nanopb/nanopb/blob/master/tests/common/person.proto

and the documentation

https://jpa.kapsi.fi/nanopb/docs/concepts.html#data-types

--

Petteri

[Jen Scrivener]

Brilliant, that's just what I was after. Thank you!

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