Specifying the compile-time option -CB causes a check at runtime that array subscript values, subscript values of elements selected from an array section, and character substring references are within bounds. Selection of the option causes code to be generated for each array or character substring reference in the program.
At runtime the code checks that the address computed for a referenced array element is within the address range delimited by the first element of the array and the last element of the array. Note that this check does not ensure that each subscript in a reference to an element of a multidimensional array or section is within bounds, only that the address of the element is within the address range of the array.
For assumed-size arrays, only the address of the first element of the array is used in the check; the address of the last element is unknown.
When -CB is selected, a check is also made that any character substring references are within the bounds of the character entity referenced.