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+TCP 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+TCP 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.
|
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+TCP 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