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PWD004: Out-of-memory-bounds array access

Issue​

A position outside the bounds of the array memory is being accessed which results in undefined behavior most likely causing invalid memory accesses and crashes.

Actions​

Fix the array access so that only positions within the array memory bounds are accessed.

Relevance​

An array is essentially a collection of items that can be randomly accessed through an integer index. Obviously, only a subset of the possible integer values will correspond to array element positions; accessing an array using index values outside that subset will access a memory position not associated with any array element. This is called an out-of-memory-bounds access and has undefined behavior in C/C++, most likely causing invalid memory accesses and crashes.

Code example​

C​

The following code uses an integer index ranging from 1 to 100 to access the array A:

void foo() {
  int A[100];
  for (int i = 0; i < 100; i++) {
    A[i + 1] = 1;
  }
}

This is incorrect since the array positions in C range from 0 to 99. Thus, the array accesses must be fixed to prevent invalid memory accesses during runtime. For instance, we can modify the array reference from A[i + 1] to A[i]:

void foo() {
  int A[100];
  for (int i = 0; i < 100; i++) {
    A[i] = 1;
  }
}

Fortran​

The following code uses an integer index ranging from 2 to 101 to access the array A:

subroutine example()
  integer :: A(100)
  integer :: i

  do i = 1, size(A, 1)
    A(i + 1) = 1
  end do
end subroutine example

This is incorrect since the array positions in Fortran range from 1 to 100. Thus, the array accesses must be fixed to prevent invalid memory accesses during runtime. For instance, we can modify the array reference from A(i + 1) to A(i):

subroutine example()
  integer :: A(100)
  integer :: i

  do i = 1, size(A, 1)
    A(i) = 1
  end do
end subroutine example

References​