Accessing an array element inside a struct (which is part of an array of structs) (in C)

Question

I want to create an array of structs, though the no. of structs in the array is read from a file / input from user.

I declare a struct:

struct student{
    char name[16];
    int *available;
    int sum;
};

typedef struct student ST;

I allocate memory for the array of structs (after getting the input of size):

ptr = (ST*)calloc(lines, sizeof(ST));

I also allocate space for each array in each struct (using a loop):

ptr->available = (int*)calloc(lines, sizeof(int));

NOW - I want to put values in these arrays. How do I reach each element?

I tried:

*((ptr+i)->(available+j)) = 1;

But the compiler tells me: error: expected identifier before ‘(’ (i and j are indexes I use, i for the i'th struct, and j for the j'th element of the array).

What am I doing wrong?

Bathsheba · Accepted Answer · 2016-08-18 11:33:25Z

4

Consider using array index notation for readability:

ptr[i].available[j] = 1;

(The equivalent syntax using explicit pointer arithmetic is the considerably more obfuscated *((ptr + i)->available + j) = 1;)

answered Aug 18, 2016 at 11:33

Bathsheba

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Jonathan Leffler · Accepted Answer · 2016-08-18 11:34:29Z

1

Forget the *(ptr + idx) notation; it's used to confuse beginners, not in 'real code'. However, if you must use it, then:

*((ptr+i)->available+j) = 1;

But use:

ptr[i].available[j] = 1;

answered Aug 18, 2016 at 11:34

Jonathan Leffler

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