getservent

Name

getservent, getservbyport, getservbyname, setservent, endservent
- get service entry

Library

libc.lib

Synopsis

#include <netdb.h>

struct servent * getservent

struct servent * getservbyname (const char *name, const char *proto);

struct servent * getservbyport (int port, const char *proto);

void setservent (int stayopen);

void endservent (void);

Return values

getservent, getservbyname and getservbyport functions return the servent structure, or a NULL pointer if an error occurs or the end of the file is reached.

Detailed description

The getservent, getservbyname, and getservbyport functions each return a pointer to an object with the following structure containing the broken-out fields of a line in the network services data base, c:/sys/data/services.

struct  servent {
        char    *s_name;        /* official name of service */
        char    **s_aliases;    /* alias list */
        int     s_port;         /* port service resides at */
        char    *s_proto;       /* protocol to use */
};

The members of this structure are:

s_name	The official name of the service.
s_aliases
	A zero terminated list of alternate names for the service.
s_port	The port number at which the service resides. Port numbers are returned in network byte order.
s_proto	The name of the protocol to use when contacting the service.

The getservent function reads the next line of the file, opening the file if necessary.

The setservent function opens and rewinds the file.

The endservent function closes the file.

The getservbyname and getservbyport functions sequentially search from the beginning of the file until a matching protocol name or port number (which must be specified in network byte order) is found, or until EOF is encountered. If a protocol name is also supplied (non- NULL ), searches must also match the protocol.

Examples

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
Char *service=”http”;
Char *protocol=”tcp”:
Struct servent *p=0;
P=getservbyname(service,protocol);
if(p!=NULL)
printf(“service not supported:);
else
printf(“Service  supported”);
return 0;
}

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
struct servent *p;
char *protocol=”tcp”;
int port;
port=htons(80);
p=(port,protocol);
if(p)
{
Printf(“port is  assigned”);
else
printf(“port is not assigned”);
}

Output

Port is assigned

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
Int main()
{
struct servent *p;
p=getservent();
if(p)
printf(“getservent successful”);
else
printf(“getservent failed”);
return 0;
}

Output

Getservent passed

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
int stayopen=1;
retservent(stayopen):
return 0;
}

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
struct servent *p;
  p=getservent();
if(p)
endservent();
return 0;
}

Files

`c:/system/data/services`

Diagnostics

Null pointer (0) returned on EOF or error.

The getservent, getservbyport, getservbyname, setservent, and endservent functions appeared in BSD 4.2.

Bugs

These functions use a thread-specific data storage; if the data is needed for future use, it should be copied before any subsequent calls overwrite it. Expecting port numbers to fit in a 32 bit quantity is probably naive.

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