What is the difference between a string and a string buffer?

Answer 1

A string, in its most fundamental representation, is simply an array of characters. The language may or may not allow its contents to be modified in place, but its length can never change (just like any other array), short of changing one of the middle characters to NUL to hide the later ones.

String buffers, on the other hand, use some technique under the hood to produce the appearance that a string is being lengthened or shortened. Perhaps a string is spliced and concatenated as necessary to produce derivative strings which then replace it within the object, or maybe an expandable list, such as a vector or a linked list, of characters are combined into a string as necessary. These are implementation details whose efficiencies are surely different, but they produce the same effect.

In higher-level languages, the syntax often suggests that a string's length is changing, but this is just a variation of the first technique above: When one string is concatenated to another or spliced, a new string is produced and returned as the expression's value and typically assigned to the same variable as the original. If these operations were to modify the internal representation, this would be a true string buffer; otherwise it is only a string with syntactic sugar.