pointers in structures with missing members - EXAMPLE

Projects Programming
1

structured data with some missing members that i would like to treat as a zero when data goes into a function. i can declare a new variable with value zero and reference that with the pointer, but it feels sloppy. any way to put a 0 value in? compiler won't let me put & in front of 0, and without it, the address gets returned. thx.

see row 2 column 2:

uint32_t one = 1;
uint32_t two = 2;
uint32_t three = 3;

typedef struct
  {
    uint32_t *colum1;
    uint32_t *column2;
    uint32_t *column3;
  }
  DATA;
  
  DATA data[]=
  {
    {&one,    &two, &one},
    {&three,  0,    &two}
  };

void setup() {
  
Serial.begin(9600);
Serial.println(*data[0].column2);
Serial.println(*data[1].column2);
    
}

void loop() {
    
}
2

If you initialize it to NULL (which I think is the same as '(void *)0'), you can check to see if the pointer is valid before using it. Maybe like this:

uint32_t one = 1;
uint32_t two = 2;
uint32_t three = 3;

typedef struct
  {
    uint32_t *column1;
    uint32_t *column2;
    uint32_t *column3;
  }
  DATA;
  
  DATA data[]=
  {
    {&one,    &two, &one},
    {&three,  NULL,    &two}
  };

void setup() 
{  
    Serial.begin(9600);
    while(!Serial);
    Serial.println(*data[0].column2, HEX);
    if( data[1].column2 == NULL )
        Serial.println( "NULL" );
    else
        Serial.println(*data[1].column2, HEX);

    data[1].column2 = &two;
    if( data[1].column2 == NULL )
        Serial.println( "NULL" );
    else
        Serial.println(*data[1].column2, HEX);
    
    
}

void loop() 
{
    
}
3

THANK YOU !!

i played with NULL, but i was trying to dereference the value of NULL in the IF statement. this worked great

4

NULL was a catch all for 'empty value' in C and can still be used.

C++11 corrected this catchall by introducing a new keyword to serve as a distinguished null pointer constant: nullptr. It is of type nullptr_t, which is implicitly convertible and comparable to any pointer type or pointer-to-member type. It is not implicitly convertible or comparable to integral types, except for bool.