How to get number of elements in array of structs-CodePudding

I have an array of sruct sockaddr_in:

struct sockaddr_in saddrlist[MAX] = {0};

the array is also being updated from external sources with memcpy, so thats the point where i dont know anymore about the count. and currNumOfelements.

Now at some point, i want to check how many elements are in the array. What I tried:

printf("before: %d",getsize(saddrlist));
memcpy(&myotherlist, saddrlist, sizeof(saddrlist) * MAX);
printf("after: %d",getsize(saddrlist));

Which results in:

before: 52448
after:  52448

int getsize(struct sockaddr_in saddrlist[10])
{
    uint8_t numOfElements = 0;
    for (size_t i = 0; i < MAX; i  )
        if (saddrlist[i] != 0)
            numOfElements  ;
}

This obviously doesn't work because if (saddrlist[i] != 0) is an invalid comparison.. but how do i do it then? I get so confused using c..

CodePudding user response：

You can use your variable currNumOfElements to determine how many elements are in the array. Because it's static array, saddrlist will always have MAX elements in it. You get to decide what's a 'valid' configuration for your struct, and what's 'invalid'.

CodePudding user response：

You could try to memcmp the addresses to a zero initialized one:

int getsize(struct sockaddr_in *saddrlist)
{
    int numOfElements = 0;
    struct sockaddr_in zero = { 0 };  // declare a local "null" sockaddr_in
    for (size_t i = 0; i < MAX; i  ) {
        if (memcmp(saddrlist   i, &zero, sizeof(zero)) != 0)
            numOfElements  ;
        else break;                   // stop at first "null" address
    }
    return numOfElements;
}