I think you could download BSEC1.x that had C language example. Then you don't need migrate BSEC2.X arduino project to C project, and avoid some problems.
After you download it, you could refer "examples\bsec_iot_example.c" file.
I have a similar problem using a BME688 ,BSEC 22.214.171.124 and the BME68X C API from GitHub
Whenever I try to subscribe the BSEC_OUTPUT_GAS_ESTIMATE_1, bsec_update_subscription returns an error.
I tried all the BSEC_SAMPLE_RATE macros as well as 1 divided by the duration of the heater profile.
As I understand it, the sample rate is the amount of samples per second.
Therefore for a heater profile with a total duration of 100 ms the sample rate should be 1000 ms / 100 ms = 10.
But if i subscribe the gas estimate with this sample rate I recieve the error -12 by the bsec_update_subscription function.
I have also recieved error -10.
The sample_rate of the requested output (virtual) sensor passed to bsec_update_subscription() does not match with the sampling rate allowed for that sensor
For testing I exported an alogrithm from AI Studio and I use the .config file to call bsec_set_configuration but the gas estimates are always at 0.0 with 0 acccuracy.
So here are my questions
1.There was integration guide document under "integration_guide" folder as you have downloaded BSEC126.96.36.199 package. You could see sampling rate selection in document.
2, 3. In "BME AI-Studio document", it supported to export the algorithm as BSEC configuration file. Refer BME688 integration guide document for how to use it in your project.