Exports never seem to get the path variables setup correctly. Did you search your whole project folder for:

#define STM_MODE_IT_FALLING

After an export I normally need to type in all the paths inside mbed-os folder so the compiler knows where to look, which is long and tedious process:

Properties > C/C++ General > Paths and Symbols > Includes

I found it at this path for your board:

mbed-os\hal\targets\hal\TARGET_STM\TARGET_STM32L4\TARGET_NUCLEO_L476RG\PinNames.h

I use mbed-dev. I don't have the same folder structure .. and the file you mentioned dosen't exist. Really, I don't know which version of mbed library I should use. There are so many different version you will be confused. Shall I use mbed-os? what is the difference between mbed-dev and mbed-os? Sure, there are many other macro and definitions that you need to tell Eclipse .. Iknow but this symbol I cannot find it in any file. I searched the whole project .. dosen't exist. PLEASE, PLEASE clean up the libraries and delete what is just an old copy of the mbed library .. Please

here is the home page of the library https://developer.mbed.org/users/mbed_official/code/mbed-dev/

Now, when I export the project, it fails to compile (using the mbed-os) since the mbed_config.h file is not generated. This is my third week that I try to build eclipse environment for my porject. It sucks how bad this process is. I don't know..A continuous bugs .. I try this, it gives me a bug, I try that, it gives me another bug...OMG.

Not just that. The project suddenly dosent compile on mbed.org .. It gives a strange fault Error: Class "FATFileSystem" has no member "_ffs" in "SDFileSystem/FATFileSystem/ChaN/diskio.cpp", Line: 25, Col: 37

While it is correct. I copied from my old copy of the project the mbed_config.h to the root of the directory, and GCC can compile the project while mbed.org cannot. It is just not explainable.