Strange variable-sized array declaration

Question

Reading this Skip List implementation I came across this code fragment:

typedef struct nodeStructure{
    keyType key;
    valueType value;
    node forward[1]; /* variable sized array of forward pointers */
    };

To me it seems that forward[1] denotes a one element array. And the comment calls it a variable sized array.

Do I misunderstand something or this is just a mistake in the source I'm reading?

Answer 1

It is called the struct hack. It is the old form of the flexible array member introduced in C99.

This has been used in the past to mimic a variable array in the last member of a structure but it is not a strictly conformning construct in C.