What is Variable Length String Format in Computer Programming: C Language

As the name implies, variable–length strings don’t have a pre-defined length. In this string, neither the precise length nor maximum length is known at the time of creating it. The array storage structure for a string can expand or shrink to accommodate any number of characters. But, there should be a mechanism to indicate the end of the string. The two common techniques to implement variable length strings are described in the article.

Length Controlled String

A length controlled string is a string whose length is stored as part of the string itself. This technique uses a count that specifies string length. The count is normally stored as the first byte followed by the string. This count is used by the string manipulation functions to determine the actual length of the string data.
For example, the strings "DOT" and "PROGRAM" are stored using length controlled format are:

Note: The first byte contains string length. Since its length is 1 byte (* bits) w can have a string length whose range is from 0 to 255. So, the string length should not exceed 255 characters.

The disadvantages can be overcome using delimited string. As we use various delimiters such as semicolons, colon, comma, period (.), in a sentence in English, the string can also be ended with delimiters.

Delimited String

In a variable length string, the string ends with a delimiter NULL (denoted by '0') character. This string which ends with a delimiter denoting the end of the string is called delimited string.

For example, the string "DOT" and "PROGRAM" are stored using a delimiter as shown here.