Obsolete Features

COMMON Block

• establishes a block of storage between programme units which declare it;
• compare with use of MODULE to provide global variables;
• common variables necessarily declared in each programme unit;
• compiler does not check that declarations are the same;
• mistakes all too easy;
• linear memory usage necessary (cf. C arrays) --- innefficient.

REAL A(50), B(20), C COMMON/Block1/A,B,C

EQUIVALENCE Block

REAL, A(100), B(100) COMPLEX Z(50) EQUIVALENCE(A(1), Z(1)), (A(2),B(1))

• Odd-numbered elements of A refer to real parts of elements of Z while even-numbered elements of A refer to imaginary parts of elements of Z;
• odd-numbered elements of of B refer to imaginary parts of elements of Z...

SEQUENCE

This forces derived types into linear storage allowing them to be used in, e.g., COMMON blocks --- don't!