- Two kinds of access to external files are defined in this subclause:
sequential access and direct access. The corresponding file types and the
associated operations are provided by the generic packages Sequential_IO and
Direct_IO. A file object to be used for sequential access is called a
sequential file, and one to be used for direct access is called a direct
file. Access to stream files is described in A.12.1.
- For sequential access, the file is viewed as a sequence of values that
are transferred in the order of their appearance (as produced by the program
or by the external environment). When the file is opened with mode In_File
or Out_File, transfer starts respectively from or to the beginning of the
file. When the file is opened with mode Append_File, transfer to the file
starts after the last element of the file.
- For direct access, the file is viewed as a set of elements occupying
consecutive positions in linear order; a value can be transferred to or from
an element of the file at any selected position. The position of an element
is specified by its index, which is a number, greater than zero, of the
implementation-defined integer type Count. The first element, if any, has
index one; the index of the last element, if any, is called the current size;
the current size is zero if there are no elements. The current size is a
property of the external file.
- An open direct file has a current index, which is the index that will be
used by the next read or write operation. When a direct file is opened, the
current index is set to one. The current index of a direct file is a
property of a file object, not of an external file.
- The Generic Package Sequential_IO
- File Management
- Sequential Input-Output Operations
- The Generic Package Direct_IO
- Direct Input-Output Operations
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