Chapter 5: Programming Practices - TOC - 5.9 ERRONEOUS EXECUTION AND BOUNDED ERRORS

5.9.7 Direct_IO and Sequential_IO

guideline

Ensure that values obtained from Ada.Direct_IO and Ada.Sequential_IO are in range.

Use the 'Valid attribute to check the validity of scalar values obtained through Ada.Direct_IO and Ada.Sequential_IO.

rationale

The exception Data_Error can be propagated by the Read procedures found in these packages if the element read cannot be interpreted as a value of the required subtype (Ada Reference Manual 1995, §A.13). However, if the associated check is too complex, an implementation need not propagate Data_Error. In cases where the element read cannot be interpreted as a value of the required subtype but Data_Error is not propagated, the resulting value can be abnormal, and subsequent references to the value can lead to erroneous execution.

notes

It is sometimes difficult to force an optimizing compiler to perform the necessary checks on a value that the compiler believes is in range. Most compiler vendors allow the option of suppressing optimization, which can be helpful.