z/OS XL C/C++ environment variables for configuration files

A z/OS® XL C/C++ environment variable is an identifier used like a variable in a program. In Table 1, the following environment variables appear:

HOSTALIASES: The host aliases data set, file, or ddname.
RESOLVER_CONFIG: The resolver configuration data set, file, or ddname. The RESOLVER_CONFIG environment variable is used by TCP/IP to include the name of an MVS data set or z/OS UNIX file in the search order for TCPIP.DATA.
RESOLVER_IPNODES: The IPNODES data set, file, or ddname.
X_SITE and X_ADDR: The HOSTS.SITEINFO and HOSTS.ADDRINFO data sets or ddnames created by the MAKESITE TSO command. The X_SITE environment variable influences how gethostbyname() resolves the network address of the specified host name. The X_ADDR environment variable is used by some TCP/IP functions, such as getnetbyaddr(), to include the name of an MVS data set or z/OS UNIX file in the search order for the HOSTS.ADDRINFO data set.
X_XLATE: The ASCII-EBCDIC translate table data set or ddname created by the CONVXLAT TSO command. The X_XLATE environment variable is used by TCP/IP to include the name of an MVS data set or z/OS UNIX file in the search order for the STANDARD.TCPXLBIN data set.

Other environment variables that can be explicitly set by the resolver include the following variables:

LOCALDOMAIN: Defines the domain origin. When this environment variable is set, it overrides any setting for DOMAIN, DOMAINORIGIN, or SEARCH found in TCPIP.DATA
RESOLVER_TRACE: Defines the data set, file, or ddname into which the resolver trace output is written.
MESSAGECASE: Determines whether messages are translated to all uppercase characters before being sent to the console.; Restriction: For IBM® z/OS Container Platform environments, RESOLVER_TRACE is the only valid environment variable. All other environment variables are ignored.