Array section bounds checking fails when paginating large allocatable arrays in Fortran

Array Section Bounds Checking Failure During Pagination

When implementing pagination for large datasets in Fortran, developers typically use array slicing with calculated offsets to access specific page ranges. For example, given a large allocatable array data(n_total), a page starting at index offset = (page-1)*page_size + 1 with size page_size would be accessed as data(offset:offset+page_size-1).

Constraint: The Fortran standard does not require runtime bounds checking for array sections, meaning out-of-bounds access in a slice results in undefined behavior unless compiler-specific flags like -fcheck=all are enabled. This creates uncertainty about whether a calculated offset correctly bounds the slice when offset + page_size - 1 > n_total for the final page.

Unresolved behavior: When the page size does not evenly divide the total records, the final page slice may extend beyond the array bounds. Different compilers may handle this differently—some may trap at runtime with bounds checking enabled, while others may silently produce undefined behavior or memory corruption.

Questions:

1. Does the Fortran standard define any behavior for array sections that extend beyond the declared bounds of an allocatable array?
2. How do major compilers (gfortran, ifort, nagfor) differ in their handling of out-of-bounds array sections when bounds checking is disabled versus enabled?
3. Is there a portable, standards-compliant approach to ensure array section bounds remain valid without relying on compiler-specific runtime checks?