File Declaration

Formal Definition

A file declaration declares the file objects of a given file type.

Simplified Syntax

file identifier : subtype_indication [ file_open_information ];

where:

file_open_information ::= [ open file_open_kind_expression ] is file_logical_name

file_logical_name ::= string_expression

Description

The file declaration creates one or more file objects of the specified type. Such a declaration can be included in any declarative part in which the objects can be created, that is within architecture bodies, processes, blocks, packages or subprograms.

The optional parts of a declaration allow making an association between the file object and a physical file in the host file system. If these parts are attached to the declaration, the file is automatically opened for access. The optional file_open_kind_expression allows specifying how the physical file associated with the file object should be opened. The expression must have the predefined type file_open_kind value, which is declared in the standard package.

If the file_open_information is included in a given file declaration, then the file declared by the declaration is opened with an implicit call to FILE_OPEN when the file declaration is elaborated. If it is not, the file will not be opened.

If the file_open_kind_expression is not included in the file_open_information of a given file declaration, then the default value of READ_MODE is used during elaboration of the file declaration.

The file_logical_name must be an expression of predefined type STRING. The value of this expression is interpreted as a logical name for a file in the host system environment. The file_logical_name identifies an external file in the host file system that is associated with the file object. This association provides a mechanism for either importing data contained in an external file into the design during simulation or exporting data generated during simulation to an external file.

The files can also be declared in subprograms. In this case, the behavior is slightly different. The file is opened when the subprogram is called and is automatically closed again when the subprogram returns. Hence the file object, and its association with a physical file in the host file system, is purely local to the subprogram activation.

Examples

Example 1

type IntegerFile is file of INTEGER;
file F1: IntegerFile;

In this example no implicit FILE_OPEN is performed during elaboration.

Example 2

type IntegerFile is file of INTEGER;
file F2: IntegerFile is "test.dat";

The above example presents that an implicit call to FILE_OPEN is performed during elaboration. The OPEN_KIND parameter defaults to the READ_MODE mode.

Example 3

type IntegerFile is file of INTEGER;
file F3: IntegerFile open WRITE_MODE is "test.dat";

Example 3 presents an implicit call to FILE_OPEN being performed during elaboration. The OPEN_KIND parameter defaults to the WRITE_MODE mode.

NOTE: All file objects associated with the same external file should be of the same base type.