How to pass a struct member as a pointer in a function

Question

First of all, I would like to say that I've exhaustively searched for the answer in this forum before post this question, but I didn´t find any answer.

OK, the problem is that i have a struct that is member of another (major) struct. I´ve written a function to clear the first struct (it takes a pointer to struct). I would like to use that function to clear the struct inside the major structure, but I don´t know exactly which is the correct way of doing that.

To explain it better, here is some code:

I have a structure, defined as:

typedef struct
{
    unsigned char next;
    unsigned char first;
    unsigned long data[TCP_RX_BUFFER+1]; 
}struct_circ_buff;

and a function to clear it:

void clearCircularBuffer(volatile struct_circ_buff *circular_buffer)
{
    int i=0;

    for(i=0;i<TCP_RX_BUFFER+1;i++)
        circular_buffer->data[i]=0;

    circular_buffer->first=0;
    circular_buffer->next=0;
}

Then, I have another struct which includes struct_circ_buff:

typedef struct 
{
    volatile unsigned char sensorType;
    volatile uint16_t  sensorFlag;
    volatile struct_circ_buff st_circular_buffer;
}struct_sens;

and I would like to write a function that would clean this struct, using the 'clearCircularBuffer' function written above. How could I do that?

void clear_sensors_struc (volatile struct_sens *sensors_struct)
{

sensors_struct->sensorFlag=0;
sensors_struct->tipoSensor=0;

    //NOW, HOW CAN I USE clearCircularBuffer to clean sensors_struct->                      
    //st_circular_buffer??

    //this way compiles fine, but i don´t think it´s correct
    clearCircularBuffer(&(sensors_struct->st_circular_buffer));

    //this way wouldn´t even compile
    clearCircularBuffer(sensors_struct->st_circular_buffer));
} 

Finally, i have a variable declared as:

struct_sens struct_sensores[MAX_NUMBER_OF_SENSORS];

and I would like to write a function that would clean that array of structures... So how could I use 'clear_sensors_struc' function to do that?

void clear_sensors_struc_array(struct_sens *sensors_struct)
{
    struct_sens aux_str[MAX_NUMBER_OF_SENSORS];  
    int i=0;    

    for(i=0;i<MAX_NUMBER_OF_SENSORS;i++)
    {         
        clear_sensors_struc(&aux_str[i]);
        *(sensors_struct+i)=aux_str[i];
    }
}

Is there any way of doing that without defining an internal struct_sens aux_str?

OK, hope someone can help me! Thanks in advance!

Answer 1

Inside the function clear_sensors_struc , it is indeed correct to do:

//this way compiles fine, but i don´t think it´s correct
clearCircularBuffer(&(sensors_struct->st_circular_buffer));

It's right because (inside function clear_sensors_struc ):

• sensors_struct : is a pointer to a struct.
• sensors_struct->st_circular_buffer : dereferences sensors_struct (using -> ) and allows you to access its member st_circular_buffer .
• &(sensors_struct->st_circular_buffer) : is a pointer to the member st_circular_buffer of struct sensors_struct that happens to be a struct struct_circ_buff .

As the function clearCircularBuffer requires a pointer, it will compile and work right.

Regarding the function to clean the array of structs, what about this?:

void clear_sensors_struc_array(struct_sens *sensors_struct)
{
    int i=0;    

    for(i=0;i<MAX_NUMBER_OF_SENSORS;i++)
    {         
        clear_sensors_struc((sensors_struct+i));
    }
}

Answer 2

In Nicolas eg clearCircularBuffer(&(sensors_struct->st_circular_buffer));

we can directly use

clearCircularBuffer(&sensors_struct->st_circular_buffer);

-> gets precedence over &

Answer 3

1)First of all you have not defined the structures correctly. define the structures as below

 typedef struct one
 {
   unsigned char next;
   unsigned char first;
   unsigned long data[11]; 
 }struct_circ_buff;

 typedef struct two
 {
   volatile unsigned char sensorType;
   volatile int  sensorFlag;
   volatile struct_circ_buff st_circular_buffer;
 }struct_sens;

2)And you asked

I would like to write a function that would clean this struct, using the 'clearCircularBuffer' function written above. How could I do that? you can do it as below

void clear_sensors_struc (volatile struct_sens *sensors_struct)
{

  int i;

  sensors_struct->sensorFlag=0;
  sensors_struct->sensorType=0;
  sensors_struct->st_circular_buffer.next=0;
  sensors_struct->st_circular_buffer.first=0;

  for(i=0;i<TCP_RX_BUFFER+1;i++)
  {
     sensors_struct->st_circular_buffer.data[i]=0;
  }    

}