Long String Types

A long string variable occupies four bytes of memory which contain a pointer to a dynamically allocated string. When a long string variable is empty (contains a zero-length string), the string pointer is nil and no dynamic memory is associated with the string variable. For a nonempty string value, the string pointer points to a dynamically allocated block of memory that contains the string value in addition to a 32-bit length indicator and a 32-bit reference count. The table below shows the layout of a long-string memory block.

Long string dynamic memory layout

Offset

Contents

-8 32-bit reference-count

-4

length in bytes

0..Length -

Icharacter string

Length

NULL character

The NULL character at the end of a long string memory block is automatically maintained by the compiler and the built-in string handling routines. This makes it possible to typecast a long string directly to a null-terminated string.

For string constants and literals, the compiler generates a memory block with the same layout as a dynamically allocated string, but with a reference count of -1. When a long string variable is assigned a string constant, the string pointer is assigned the address of the memory block generated for the string constant. The built-in string handling routines know not to attempt to modify blocks that have a reference count of -1.

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Project Management Made Easy

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