appends

Append, or appends, is a programming and data-management operation that adds data to the end of a sequence, collection, or file. It is commonly used with strings, lists, arrays, and log files, and is the counterpart to prepend, which inserts at the start.

In data structures, appending grows the container by placing new elements after existing ones. In languages with immutable strings, appending typically creates a new string rather than modifying the old one in place; performance considerations lead developers to use builders or join operations when constructing large strings. For lists and arrays, many languages provide explicit append or add methods (for example, Python's list.append and list.extend; Java's StringBuilder.append; JavaScript's Array.push).

In file handling, appending means writing data to the end of a file without truncating existing content. This is enabled by opening the file in append mode (for example, in Python with open('file','a'), or in C with fopen(..., 'a')). In databases and logs, appending inserts new records at the end of the log or log-structured storage, preserving previous entries.

Performance and correctness depend on the data type and environment. Repeated string concatenation can be costly; using builders, buffers, or append-efficient structures reduces overhead. Prepending or inserting in the middle may require different algorithms and data structures, with different performance characteristics.

See also: concatenation, insertion, extension, extend.