There are several possible options, which are appropriate under different circumstances:

Ropes

Use the rope package provided by the SGI STL. This provides all functionality that's likely to be needed. Its interface is similar to the current draft standard, but different enough to allow a correct and thread-safe implementation. It should perform reasonably well for all applications that do not require very frequent small updates to strings. It is the only alternative that scales well to very long strings, i.e. that could easily be used to represent a mail message or a text file as a single string.

The disadvantages are:

• Single character replacements are slow. Consequently STL algorithms are likely to be slow when updating ropes. (Insertions near the beginning take roughly the same amount of time as single character replacements, and much less time than corresponding insertions for the other string alternatives.)

• The rope implementation stretches current compiler technology. Portability and compilation time may be an issue in the short term. Pthread performance on non-SGI platforms will be an issue until someone provides machine-specific fast reference counting code. (This is also likely to be an issue for other reference counted implementations.)

C strings

This is likely to be the most efficient way to represent a large collection of very short strings. It is by far the most space efficient alternative for small strings. For short strings, the C library functions in provide an efficient set of tools for manipulating such strings. They allow easy communication with the C library. The primary disadvantages are that

• Operations such as concatenation and substring are much more expensive than for ropes if the strings are long. A C string is not a good representation for a text file in an editor.

• The user needs to be aware of sharing between string representations. If strings are assigned by copying pointers, an update to one string may affect another.

• C strings provide no help in storage management. This may be a major issue, although a garbage collector can help alleviate it.

vector

If a string is treated primarily as an array of characters, with frequent in-place updates, it is reasonable to represent it as vector or vector. The same is true if it will be modified by STL container algorithms. Unlike C strings, vectors handle internal storage management automatically, and operations that modify the length of a string are generally more convenient.

Disadvantages are:

• Vector assignments are much more expensive than C string pointer assignments; the only way to share string representations is to pass pointers or references to vectors.

• Most operations on entire strings (e.g. assignment, concatenation) do not scale well to long strings.

• A number of standard string operations (e.g. concatenation and substring) are not provided with the usual syntax, and must be expressed using generic STL algorithms. This is usually not hard.

• Conversion to C strings is currently slow, even for short strings. That may change in future implementations.