Thread: Passing a pointer to struct array

I have a struct

Code:

typedef struct
{
   char *name;
   float value;
   void *pntr;
   uint8_t found;
}DICTIONARY;

Initialize it

Code:

static DICTIONARY pid_dict[] = 
{
    {"-p" ,  0, 0, 0 },
    {"-i" ,  0, 0, 0 },
    {"-d" ,  0, 0, 0 },
    {"-max", 0, 0, 0 },
    {"-min", 0, 0, 0 },
    {"-var", 0, 0, 0 },
};

Function to work with the struct

Code:

uint32_t ParseDictionary(DICTIONARY *dict[], char** args, uint32_t argc)
{
    uint32_t dict_len = (sizeof (dict)/sizeof (dict[0]));
    
    uint32_t i, j;
    float val;
    
    for (i = 0; i < argc; i++)
    {
        for (j = 0; j < dict_len; j++)
        {
            if (strcmp(args[i], dict[j]->name)==0)
            {
                if (IsFloat(args[i+1]))
                {
                    val = atof(args[i+1]);
                    dict[j]->value = val;
                    dict[j]->found = 1;
                }
                else
                    return MSG_INV_ARG;
            }
        }
    }
    
    return MSG_OK; 
}

Now I want to pass it to a function

Code:

ParseDictionary(&pid_dict, &args[1], argc);

I get - Error[Pe167]: argument of type "DICTIONARY (*)[6]" is incompatible with parameter of type "DICTIONARY **"
And this way

Code:

ParseDictionary(&pid_dict[0], &args[1], argc);

I get -Error[Pe167]: argument of type "DICTIONARY *" is incompatible with parameter of type "DICTIONARY **"

What is wrong?

You have an array of DICTIONARY objects, so when you pass it as an argument, it is converted to a pointer to its first element. Hence, you should declare your function like this:

Code:

uint32_t ParseDictionary(DICTIONARY dict[], uint32_t dict_len, char** args, uint32_t argc)
{

Then call it like this:

Code:

ParseDictionary(pid_dict, sizeof(pid_dict) / sizeof(pid_dict[0]), &args[1], argc);

I added the dict_len parameter because your approach of using sizeof to compute the array length simply won't work within the function as the dict parameter is a pointer, despite the apparent use of array notation to declare it.

You should be aware that the type of the result of sizeof is size_t, which is not necessarily equivalent to uint32_t.

Also, it is a common convention to use fully uppercase names for constants and/or macros. Consequently, you might wish to rename DICTIONARY to Dictionary.

Originally Posted by john7

I can not iterate - on dict[j]->name I get Error[Pe044]: expression must have pointer type

That's because you're trying to treat dict[j] as a pointer when it is an object. Write dict[j].name instead.

Originally Posted by john7

I pass it by value - a local copy - I can not modify a member - dict[j]->value = val; only a local copy dict[j].value = val;

C only has pass by value semantics. Pass by reference can still be done through a pointer... and that's exactly what you're doing here, so you're mistaken when you say that you're dealing with "a local copy".