ESP8266 Platform TCP Client example

H All,
I am new to Platform IO and is trying to have a quick start. I am experiencing a hard learning time as I couldn’t find example on TCP Client that works on ESP8266 RTOS SDK framework. Those that I can find are using Arduino framework in which I am not planning to use it.
I encountered lots of header files, missing include files errors as I do not know why GitHUB and platformIO installed SDK are different. So things do not match.
I hope someone can lift me from this stuck position.
Thanks in advance.

I would not recommend using PlatformIO with ESP8266-RTOS-SDK as the framework because the ESP8266-RTOS-SDK version PlatformIO uses is beyond very outdated. See Update ESP8266_RTOS_SDK v1.4.0 to ESP8266_RTOS_SDK v3.x.x · Issue #219 · platformio/platform-espressif8266 · GitHub.

If you do, you must refer to the documentation of that old 1.4.0 version.