How to "share" (extern) a structure in my code?

[mr_monster]

I'm writing a driver for communicating with a DAC, this will run on an ARM processor. The SPI communication initializes a structure called hspi3 and it hold various settings for the SPI hardware. I don't care much about this structure, however the command I use for sending a byte over SPI needs to have access to this structure.

Here is the SPI sending command:

HAL_SPI_Transmit(&hspi3,(uint8_t*)aTxBuffer,3,1000);

The 1st argument is the structure.

Now here is the problem. My driver library is located in a seperate C file with its own header. My code in that C file can not see the structure that is generated in init code placed in the main C file because it is defined as follows:

SPI_HandleTypeDef hspi3;

How can I make this structure visible in my library?

[migf1]

Deleted (I just realized my answer was irrelevant to the question)

So, on a second attempt from my part, declaring: extern SPI_HandleTypeDef hspi3; in your library does not work?

[mr_monster]

Of course that should work, however the code including the deceleration statement is automatically generated by a software and in case I will change settings it will be re-written. Can I somehow make a pointer to that structure external and just use that?

[migf1]

Unfortunately I'm not familiar with your codebase, nor the SPI. Isn't the type SPI_HandleTypeDef publicly exposed, via a header for example? If so, your library could use arguments of that type in the functions that need to manipulate objects of that type.

[mr_monster]

Actually it does not matter what SPI is... The structure type is SPI_HandleTypeDef and it is defined in a header which indeed has public privileges. The thing is that I need to use the specific instance that is created in main, which I showed before, declared as private. I somehow need to be able to point at it. I guess an option would be to create a copy of the structure but since all structure manipulation is taken care of by the SPI library I can't be sure that my copy is up to date and I don't want to modify the SPI library or write a function that would be called repeatedly to compare my copy structure with the original one.

[migf1]

Actually it does not matter what SPI is... The structure type is SPI_HandleTypeDef and it is defined in a header which indeed has public privileges. The thing is that I need to use the specific instance that is created in main, which I showed before, declared as private. I somehow need to be able to point at it. I guess an option would be to create a copy of the structure but since all structure manipulation is taken care of by the SPI library I can't be sure that my copy is up to date and I don't want to modify the SPI library or write a function that would be called repeatedly to compare my copy structure with the original one.

I kinda lost you!

Since SPI_HandleTypeDef is a public type, which you instantiate in your main.c file, what stops you from passing a pointer to that instant as an argument to a function of your own library? Your library function gets access directly to that particular instance of SPI_HandleTypeDef.

// main.c
#include "spi.h"
#include "mylib.h"
...
int main( void )
{
    SPI_HandleTypeDef hspi3;
    mylib_foo( &hspi3, ... );
    ...
}

// mylib.h
...
#include "spi.h"
...
whatever mylib_foo( SPI_HandleTypeDef *, ... );
...

// mylib.c
#include "spi.h"
...
whatever mylib_foo( SPI_HandleTyleDef *handle, ... )
{
    ...
    return whatever;
}