The EXTNAME keyword is used to specify the name of the file which contains the field descriptions used as the subfield description for the data structure being defined.
The file_name parameter is required. Optionally a format name may be specified to direct the compiler to a specific format within a file. If format_name parameter is not specified the first record format is used.
The file-name and format-name parameters can be either names or character literals. If a character literal is specified, the file or format name name must be specified in the correct case. For example, if the external file is MYFILE, the file-name parameter could be specified as a name in mixed case such as myFile or myfile, but if specified as a literal it must be 'MYFILE'. If the file-name is a character literal, it can be in any of the following forms
'LIBRARY/FILE'
'FILE'
'*LIBL/FILE'
The last parameter specifies which fields in the external record to extract:
If this parameter is not specified, the compiler extracts the fields of the input buffer.
If the data structure definition contains an E in position 22, and the EXTNAME keyword is not specified, the name specified in positions 7-21 is used.
The compiler will generate the following definition specification entries for all fields of the externally described data structure:
All data structure keywords except LIKEDS and LIKEREC are allowed with the EXTNAME keyword.