// socket.h

struct skt_t {
    uint8_t         *dst_mac;
    uint8_t         *dst_ip;
    uint16_t  base_addr;
    uint16_t  tx_reg_addr;
    uint16_t  rx_reg_addr;
    uint16_t        src_port;
    uint16_t        dst_port;
    uint8_t   id;
    socket_sts      status;
    socket_protocol protocol;
    uint8_t         tx_memory_kb;
    uint8_t         rx_memory_kb;
    uint8_t         imr;
} skt_t;

void W5500_socket_init(struct skt_t *skt, socket_id socket, socket_protocol mode);
void W5500_socket_open(struct skt_t *skt);

// socket.c

struct skt_t _skt[8];

void W5500_socket_init(struct skt_t *skt, socket_id socket, socket_protocol mode)
{
    // pointing to the 'socket' element on the _skt struct
    skt = &_skt[socket];
    // changing the configuration
    skt->base_addr      = SKT_SOCKET_BASE(socket);
    skt->tx_reg_addr    = SKT_TX_BASE(socket);
    skt->rx_reg_addr    = SKT_RX_BASE(socket);
    skt->src_port       = 0x0000;
    skt->status         = SOCKET_STS_CLOSED;
    skt->protocol       = mode;
    skt->tx_memory_kb   = 2;
    skt->rx_memory_kb   = 2;
}

// here i'm trying to access a member of the skt_t struct array i previously
// accessed
void W5500_socket_open(struct skt_t *skt)
{
    if (skt->protocol == SOCKET_MODE_TCP) {
        LED_Write(1);
    }
}

// main.c

// tcp_server will be a pointer to a member of the _skt struct array
struct skt_t *tcp_server;

int main(void)
{
    // with this function i set _skt[0].protocol to SOCKET_MODE_TCP
    W5500_socket_init(tcp_server, 0, SOCKET_MODE_TCP);

    // after this function LED should be turned on
    // but it doesn't
    W5500_socket_open(tcp_server);

    while (1) {
    }
}