Read and Restore Statements

General Description

The read-statement provides for the assignment of values to variables from a sequence of data created from data-statements (see 17). The restore-statement allows the data in the program to be reread. The general syntactic forms of the read and restore statements are

READ variable, ..., variable 
RESTORE

Syntaxe

1. read-statement = READ variable-list
2. restore-statement = RESTORE

Examples

    READ X, Y, Z        READ X(l), A$, C

Semantics

The read-statement causes variables in the variable-list to be assigned values, in order, from the sequence of data (see 17). A conceptual pointer is associated with the data sequence. At the initiation of execution of a program, this pointer points to the first datum in the data sequence. Each time a read-statement is executed, each variable in the variable-list in sequence is assigned the value of the datum indicated by the pointer and the pointer is advanced to point beyond that datum.

The restore-statement resets the pointer for the data sequence to the beginning of the sequence, so that the next read-statement executed will read data from the beginning of the sequence once again.

The type of a datum in the data sequence shall correspond to the type of the variable to which it is to be assigned; i.e., numeric-variables require unquoted-strings which are numeric-constants as data and string-variables require quoted-strings or unquoted-strings as data. An unquoted-string which is a valid numeric representation may be assigned to either a string-variable or a numeric-variable by a read-statement.

If the evaluation of a numeric datum causes an underflow, then its value shall be replaced by zero.

Subscript expressions in the variable-list are evaluated after values have been assigned to the variables preceding them (i.e. to the left of them) in the list.

Exceptions

• The variable-list in a read-statement requires more data than are present in the remainder of the data-sequence (fatal).
• An attempt is made to assign a string datum to a numeric variable (fatal).
• The evaluation of a numeric datum causes an overflow (non-fatal, the recommended recovery procedure is to supply machine infinity with the appropriate sign and continue).
• A string datum contains too many characters (fatal).

Remarks

It is recommended that implementations report an underflow as exception and continue.

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