Objects of type struct netconn and
struct netbuf are intended to be used as opaque
types and the structure contents are intended to be maintained and viewed
only by lwIP itself. User applications accessing internal members do so at
their own risk, and future API compatibility is not guaranteed, nor is
thread synchronisation since lwIP is entitled to change structure contents
at any time.
Some API functions take an argument of type struct
ip_addr. The type may be accessed as if it has the following
structure:
struct ip_addr {
u32_t addr;
};
Caution
API users must use the declaration of this structure from the header file
<lwip/ip_addr.h> which is included
implicitly by <lwip/api.h>. This
type must not be declared by the application itself.
For convenience, predefined struct ip_addr instances are provided
for the special cases of "any" IP address (0.0.0.0), and the global broadcast
address (255.255.255.255). These instances can be accessed with the macro
defines IP_ADDR_ANY and IP_ADDR_BROADCAST
which return values of type struct ip_addr *.
The addr field is a 32-bit integral value representing
the IP address in network byte order (not host byte order).
A variety of convenience function-like macros exist for
manipulation or evaluation of IP addresses:
IP_ADDR_ANY
This macro evaluates to an expression of type struct ip_addr *
identifying an IP address structure which can be used to represent the special "any"
IP address 0.0.0.0.
IP_ADDR_BROADCAST
This macro evaluates to an expression of type struct ip_addr *
identifying an IP address structure which can be used to represent the special
global IP address 255.255.255.255.
IN_CLASSA(a)
An expression which evaluates to non-zero if a (of type
u32_t and in host byte order) is a class A internet address.
IN_CLASSB(a)
An expression which evaluates to non-zero if a (of type
u32_t and in host byte order) is a class B internet address.
IN_CLASSC(a)
An expression which evaluates to non-zero if a (of type
u32_t and in host byte order) is a class C internet address.
IN_CLASSD(a)
An expression which evaluates to non-zero if a (of type
u32_t and in host byte order) is a class D internet address.
IP4_ADDR(ipaddr, a, b, c, d)
Sets ipaddr (of type struct ip_addr *) to the internet
address a.b.c.d. For example:
Returns non-zero if the arguments addr1 and
addr2, both of type struct
ip_addr * are identical. Zero if they differ.
ip_addr_netcmp(addr1, addr2, mask)
Returns non-zero if the arguments addr1 and
addr2, both of type struct
ip_addr * are on the same network, as indicated by
the network mask mask which is itself also of
type struct ip_addr *. Zero if they are on
different networks.
htons(s)
Portably converts s of type u16_t
from host byte order to a u16_t in network byte order.
ntohs(s)
Portably converts s of type u16_t
from network byte order to a u16_t in host byte order.
htonl(l)
Portably converts l of type u32_t
from host byte order to a u32_t in network byte order.
ntohl(l)
Portably converts l of type u32_t
from network byte order to a u32_t in host byte order.
Some further potentially useful macro definitions can be viewed in
<lwip/ip_addr.h>.
While the BSD sockets API uses POSIX standard error codes
(ENOMEM, EINVAL, etc.)
the lwIP sequential API has its own separate set of error
code definitions.
These error definitions are used by any API function
that returns a value of type err_t. The
following table indicates possible error code values
and their meaning:
