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FreeRTOS_gethostbyname()

[FreeRTOS Embedded IP Stack API]

FreeRTOS_sockets.h
uint32_t FreeRTOS_gethostbyname( const uint8_t *pcHostName );
		

Performs a Domain Name System (DNS) lookup on a host name, returning the hosts IP address. For example, assuming a DNS server replies to the lookup request, a call to FreeRTOS_gethostbyname( "www.freertos.org" ) will return freertos.org's IP address.

ipconfigUSE_DNS must be set to 1 in FreeRTOSIPConfig.h for FreeRTOS_gethostbyname() to be available.

A DNS lookup can only be performed when FreeRTOS+UDP knows the IP address of a DNS server. If ipconfigUSE_DHCP is 0 in FreeRTOSIPConfig.h then the DNS server address is passed into FreeRTOS+UDP as a parameter of the FreeRTOS_IPInit() function. If ipconfigUSE_DHCP is 1 in FreeRTOSIPConfig.h then the DNS server address can be obtained from a DHCP server.

FreeRTOS_gethostbyname() will wait (in the Blocked state so other tasks can execute) for a reply for 200ms after each DNS request - with a maximum of 5 DNS requests being sent.

Parameters:

pcHostName   A standard NULL terminated string containing the name of the host being looked up.

Returns:

If the lookup is successful then the IP address of the host is returned in network byte order.

If the lookup fails then 0 is returned.

Example usage:


/* FreeRTOS+UDP sockets include */
#define "FreeRTOS_sockets.h"

void aFunction( void )
{
uint32_t ulIPAddress;
int8_t cBuffer[ 16 ];

    /* Lookup the IP address of the FreeRTOS.org website. */
    ulIPAddress = FreeRTOS_gethostbyname( "www.freertos.org" );
    
    if( ulIPAddress != 0 )
    {
        /* Convert the IP address to a string. */
        FreeRTOS_inet_ntoa( ulIPAddress, ( char * ) cBuffer );
        
        /* Print out the IP address. */
        printf( "www.FreeRTOS.org is at IP address %s\r\n", cBuffer );
    }
    else
    {
        printf( "DNS lookup failed. " );
    }
}

						
Example use of the FreeRTOS_gethostbyname() API function


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Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2016 Real Time Engineers Ltd.
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