(C) Revert to Default DNS Nameservers

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Demonstrates how to revert back to the default nameservers of the local system where your application is running.

Note: This example requires Chilkat v9.5.0.96 or later.

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#include <C_CkDns.h>

void ChilkatSample(void)
    {
    HCkDns dns;
    int nsCount;
    int i;
    BOOL supportsTls;

    // The only reason you would have to revert back to the local system's default nameservers
    // is if your application had previously set different nameservers, and you wish to revert back.

    // When your application starts, the DNS nameservers to be used are the default nameservers
    // configured on the system where your application is running.

    // There is one exception: Chilkat defaults to using the public Google nameservers (8.8.8.8 and 8.8.4.4) for
    // Android applications. Reverting to the default nameservers would revert to the Google nameservers.

    // However, Chilkat does not query the local system for the default nameservers unless Chilkat needs
    // to do a DNS lookup and there not yet any DNS nameservers defined.  Thus technically, when your application
    // starts, there are no default nameservers. They are auto-assigned when first needed.

    // If your application explicitly defines DNS nameservers, such as by calling AddDefaultnamervers, or AddNameserver
    // then Chilkat will not automatically auto-assign.

    dns = CkDns_Create();

    // Here we are explicitly adding the system default nameservers, because technically this application
    // has not yet done anything that would require a DNS lookup, and thus DNS nameservers are not yet defined.
    // Your default nameserver is assumed to not support TLS.
    CkDns_AddDefaultNameservers(dns);

    // Let's examine our nameservers
    nsCount = CkDns_getNumNameservers(dns);
    i = 0;
    while (i < nsCount) {
        printf("%d: %s\n",i + 1,CkDns_getNameserver(dns,i));
        i = i + 1;
    }

    // On my Windows system, the result is a single nameserver at 
    // 1: 172.16.16.16

    // ---------------------------------------------------------
    // We could add additional nameservers, such as Google and Cloudfare
    supportsTls = TRUE;
    // Cloudfare
    CkDns_AddNameserver(dns,"1.1.1.1",supportsTls);
    // Google
    CkDns_AddNameserver(dns,"8.8.8.8",supportsTls);

    // See the nameservers now used by Chilkat
    nsCount = CkDns_getNumNameservers(dns);
    i = 0;
    while (i < nsCount) {
        printf("%d: %s\n",i + 1,CkDns_getNameserver(dns,i));
        i = i + 1;
    }

    // Result:
    // 1: 172.16.16.16
    // 2: 1.1.1.1
    // 3: 8.8.8.8

    // ---------------------------------------------------------
    // To revert back to the system default nameservers, clear all
    // then re-add the default.
    CkDns_RemoveAllNameservers(dns);
    CkDns_AddDefaultNameservers(dns);

    // See the nameservers now used by Chilkat
    nsCount = CkDns_getNumNameservers(dns);
    i = 0;
    while (i < nsCount) {
        printf("%d: %s\n",i + 1,CkDns_getNameserver(dns,i));
        i = i + 1;
    }

    // Result:
    // 1: 172.16.16.16


    CkDns_Dispose(dns);

    }