Functions
Description in TCP and UDP socket programming
Before going to
understand the TCP socket programming you must have to understand the working
of various system calls and inbuilt functions that are using in programming.
Those system calls and functions ar given below.
1. Socket - creates a socket for network
communications. Returns a file
descriptor for the socket.
Syntax: int fd =
Socket (family, type, protocol)
Family- IPv4 or
IPv6
Type- TCP or UDP
Protocol: 0 not
used for internet socket.
2. Bind - used by
server process to associate an end-point address with a socket. Must include the port and server address with
this call.
Syntax: Bind(Fd,addr,addrlen)
Addr: Pointer to a
struct sockaddr
Addrlen: Size of
the struct in byte
3. Listen - used
by server process to indicate that it is ready to receive connections
Syntax: Listen(fd, backlog)
Backlog: Maximum
no of connection
4. Connect -
called by the client process to establish a connection between it and a server
process. Need the server's address and
port number.
Syntax: Connect(Fd,addr,addrlen)
Addr: Pointer to a
struct sockaddr
Addrlen: Size of
the struct in byte
5. Accept -
called by the server process to accept a connection. If no client is trying to connect the call
will block.
Syntax: accept(fd, (struct sockaddr*)NULL, NULL);
sockaddr*: An optional pointer to a buffer that receives the address of the
connecting entity, as known to the communications layer. The exact format of
the addr parameter is determined by the address family that was established when
the socket from the sockaddr structure was created.
addrlen : An optional
pointer to an integer that contains the length of structure pointed to by the addr parameter.
6.
Memset function:
The C library function void *memset(void *str, int c,
size_t n) copies the character c (an unsigned char)
to the first n characters of the string pointed to by the
argument str.
void *memset(void *str, int c, size_t n)
Parameters
·
str -- This is pointer to the block of memory
to fill.
· c -- This is the value to be set. The value
is passed as an int, but the function fills the block of memory using the
unsigned char conversion of this value.
·
n -- This is the number of bytes to be set
to the value.
Return Value
This function returns a pointer to the memory
area str.
Example
The following example shows the usage of
memset() function.
#include
#include
int main ()
{
char str[50];
strcpy(str,"This is string.h library function");
puts(str);
memset(str,'$',7);
puts(str);
return(0);
}
Let us compile and run the above program, this
will produce the following result:
This is string.h library function
$$$$$$$ string.h library function
7.
Htonal function:
#include <arpa/inet.h>
uint32_t htonl(uint32_t hostlong);
The htonl() function
converts the unsigned integer host long from host byte order to network byte
order.
8.
Htons function:
uint16_t htons(uint16_t hostshort);
The htons() function
converts the unsigned short integer host short from host byte order to network
byte order.
9.
Inet_pton function:
inet_pton - convert
IPv4 and IPv6 addresses from text to binary form
#include
int inet_pton(int af,
const char *src, void *dst);
This function converts the character string
src into a network address structure in
the af address family, then copies the network address structure to dst. The af argument must be either AF_INET or AF_INET6.
10.
Ctime function:
The C library function
char *ctime(const time_t *timer) returns a string representing the localtime
based on the argument timer.
The returned string has
the following format: Www Mmm dd hh:mm:ss yyyy Where Www is the weekday, Mmm
the month in letters, dd the day of the month, hh:mm:ss the time, and yyyy the
year.
11.
Snprintf():
snprintf is essentially
a function that redirects the output of printf to a buffer. This is
particularly useful for avoiding repetition of a formatted string. You can
build a string once and use printf("%s", mystr) instead of
print("%d,%s,%f,%d", x,y,z,a) every time, which gets cumbersome with
actual variable names.
The function header for
snprintf is
int snprintf(char *str,
size_t size, const char *format, ...);
*str is the buffer
where printf output will be redirected to. size is the maximum number of
bytes(characters) that will be written to the buffer, including the terminating
null character that snprintf automatically places for you. The format and the
optional ... arguments are just the string formats like "%d", myint
as seen in printf.
12.
Write function:
int write( int
handle, void *buffer,
int nbyte );
The write() function
attempts to write nbytes from buffer to the file associated with handle. On
text files, it expands each LF to a CR/LF. The function returns the number of
bytes written to the file. A return value of -1 indicates an error, with errno
set appropriately.
13. Fputs function:
The C library function int fputs(const char *str, FILE *stream) writes a string to the specified
stream up to but not including the null character.
int fputs(const char *str, FILE *stream)
Parameters
·
str -- This is an array containing the null-terminated sequence
of characters to be written.
·
stream -- This is the pointer to a FILE object that identifies the
stream where the string is to be written.
This
function returns a non-negative value else, on error it returns EOF.
14.
Read()
int read( int
handle, void *buffer,
int nbyte );
The read() function
attempts to read nbytes from the file associated with handle, and places the
characters read into buffer. If the file is opened using O_TEXT, it removes
carriage returns and detects the end of the file.
The function returns
the number of bytes read. On end-of-file, 0 is returned, on error it returns
-1, setting errno to indicate the type of error that occurred.
15.
Time_t data type
The time_t datatype is
a data type in the ISO C library defined for storing system time values. Such
values are returned from the standard time() library function. This type is a
typedef defined in the standard header.
16.
inet_addr()
This function converts the Internet host address from IPv4 numbers-and-dots notation into binary
data in network byte order. If the input is invalid, INADDR_NONE (usually -1) is returned. Use of this function is
problematic because -1 is a valid address (255.255.255.255).
17. sendto():
The sendto()
function shall send a message through a connection-mode or connectionless-mode
socket. If the socket is connectionless-mode, the message shall be sent to the
address specified by dest_addr. If the socket is connection-mode, dest_addr
shall be ignored.
Prototype: ssize_t sendto(int socket, const void *message,
size_t length,
int flags, const struct
sockaddr *dest_addr,
socklen_t dest_len);
The sendto() function takes the following
arguments:
Socket: Specifies the socket file descriptor.
Message:
Points to a buffer
containing the message to be sent.
Length:
Specifies the size of
the message in bytes.
Flags:
Specifies the type of
message transmission.
MSG_EOR
Terminates a record (if supported by the
protocol).
MSG_OOB
Sends out-of-band data on sockets that support
out-of-band data. The significance and semantics of out-of-band data are
protocol-specific.
dest_addr:Points to a sockaddr structure containing the
destination address. The length and format of the address depend on the address
family of the socket.
dest_len:Specifies the length of
the sockaddr structure
pointed to by the dest_addr argument.
18. Rcvfrom():
The recvfrom() function shall receive a message
from a connection-mode or connectionless-mode socket. It is normally used with
connectionless-mode sockets because it permits the application to retrieve the
source address of received data.
Prototype: ssize_t recvfrom(int socket,
void *restrict buffer, size_t length, int flags, struct sockaddr
*restrict address, socklen_t
*restrict address_len);
The recvfrom()
function takes the following arguments:
Socket:
Specifies the socket file descriptor.
Buffer: Points to the buffer
where the message should be stored.
Length:
Specifies the length in bytes of the buffer
pointed to by the buffer argument.
Flags: Specifies the type of message reception. Values of this argument
are formed by logically OR'ing zero or more of the following values:
MSG_PEEK, MSG_OOB, MSG_WAITALL
Address: A null pointer, or points to a sockaddr structure in which the
sending address is to be stored. The length and format of the address depend on
the address family of the socket.
address_len: Specifies the length of the sockaddr structure pointed to by
the address argument.
The recvfrom()
function shall return the length of the message written to the buffer pointed
to by the buffer argument. For message-based sockets.
18. Sockaddr():
The sockaddr_storage structure shall
contain at least the following members:
sa_family_t ss_family
When a sockaddr_storage structure is
cast as a sockaddr structure,
the ss_family field
of the sockaddr_storage structure
shall map onto the sa_family field
of the sockaddr structure.
When a sockaddr_storage structure
is cast as a protocol-specific address structure, the ss_family field shall map onto a
field of that structure that is of type sa_family_t and that identifies the protocol's address
family.
19. Socklen_t:
socklen_t,
which is an unsigned opaque integral type of length of at least 32 bits.
