getservbyport_r()--Get Service Name for Port Number

 #include <netdb.h>

 int getservbyport_r(int port_number,
                 char *protocol_name,
                 struct servent *servent_struct_addr,
                 struct servent_data
                    *servent_data_struct_addr)

The getservbyport_r() function is used to retrieve information about a service assigned to a port number. The information is retrieved from the service database file.

Parameters

int port_number  (input) 

Specifies the port number for which service information is to be retrieved.

char *protocol_name  (input) 

Specifies the pointer to the character string that contains the name of the protocol that further qualifies the search criteria. For example, if the port_number is 10, and the protocol_name is tcp, then the call will return the server that uses the TCP protocol on port number 10. If this parameter is set to NULL, then the first server is returned, regardless of the protocol used.

struct servent *servent_struct_addr  (input/output) 

Specifies the pointer to a servent structure where the results will be placed. All results must be referenced through this structure.

struct servent_data *servent_data_struct_addr  (input/output) 

Specifies the pointer to the servent_data structure, which is used to pass and preserve results between function calls. The field serve_control_blk in the servent_data structure must be initialized with hexadecimal zeros before its initial use. If compatibility with other platforms is required then the entire servent_data structure must be initialized with hexadecimal zeros before initial use.

Authorities

No authorization is required.

Return Value

The getservbyport_r() function returns an integer. Possible values are:

• -1 (unsuccessful call)
• 0 (successful call)

The struct servent denoted by servent_struct_addr and struct servent_datadenoted by servent_data_struct_addr are both defined in <netdb.h>. The structure struct serventis defined as:

      struct servent [
        char            *s_name;
        char            **s_aliases;
        int             s_port;
        char            *s_proto
      ];

s_name points to the character string that contains the name of the service. s_aliases is a pointer to a NULL-terminated list of pointers, each of which points to a character string that represents an alternative name for the service. s_port is the port number assigned to the service. s_proto is a pointer to a character string that contains the name of the protocol being used by the service.

Error Conditions

When the getservbyport_r() function fails, errno can be set to:

[EINVAL]

The servent_data structure was not properly initialized with hexadecimal zeros before initial use. For corrective action see the description for structure servent_data.

Usage Notes

1. System i^® Navigator or the following CL commands can be used to access the services database file:
   
   
   • WRKSRVTBLE (Work with Service Table Entries)
   • ADDSRVTBLE (Add Service Table Entry)
   • RMVSRVTBLE (Remove Service Table Entry)
   
   
2. When the service information is obtained from the service database file, the file is opened and the service information is retrieved (if it exists) from the file. The file is then closed only if a setservent_r() call with a non-zero parameter value was not previously done.
   
   
3. A coded character set identifier (CCSID) of 65535 for the job requests that no database translation be performed. For translation to occur for the protocol name specified by the protocol_name parameter, or for the service names returned in the servent structure, the job CCSID must be something other than 65535.

Related Information

• getservbyname_r()--Get Port Number for Service Name
  
  
• getservent_r()--Get Next Entry from Service Database
  
  
• setservent_r()--Open Service Database
  
  
• endservent_r()--Close Service Database

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