rope<T, Alloc>


Category: containers	Component type: type

Description

Ropes are a scalable string implementation: they are designed for efficient operation that involve the string as a whole. Operations such as assignment, concatenation, and substring take time that is nearly independent of the length of the string. Unlike C strings, ropes are a reasonable representation for very long strings such as edit buffers or mail messages. [1]

Though ropes can be treated as Containers of characters, and are almost Sequences, this is rarely the most efficient way to accomplish a task. Replacing an individual character in a rope is slow: each character replacement essentially consists of two substring operations followed by two concatenation operations. Ropes primarily target a more functional programming style.

They differ from vector<char> or reference-counted string implementations in the following ways.

Advantages:

Much faster concatenation and substring operations involving long strings. Inserting a character in the middle of a 10 megabyte rope should take on the order of 10s of microseconds, even if a copy of the original is kept, e.g. as part of an edit history. In contrast, this would take on the order of a second for conventional "flat" string representation. The time required for concatenation can be viewed as constant for most applications. It is perfectly reasonable to use a rope as the representation of a file inside a text editor.
Potentially much better space performance. Minor modifications of a rope can share memory with the original. Ropes are allocated in small chunks, significantly reducing memory fragmentation problems introduced by large blocks.
Assignment is simply a (possibly reference counted) pointer assignment. Unlike reference-counted copy-on-write implementations, this remains largely true even if one of the copies is subsequently slightly modified. It is very inexpensive to checkpoint old versions of a string, e.g. in an edit history.
It is possible to view a function producing characters as a rope. Thus a piece of a rope may be a 100MByte file, which is read only when that section of the string is examined. Concatenating a string to the end of such a file does not involve reading the file. (Currently the implementation of this facility is incomplete.)

Disadvantages:

Single character replacements in a rope are expensive. A character update requires time roughly logarithmic in the length of the string. It is implemented as two substring operations followed by two concatenations.
A rope can be examined a character at a time through a const_iterator in amortized constant time, as for vector<char>. However this is slower than for vector<char> by a significant constant factor (roughly a factor of 5 or 10 if little processing is done on each character and the string is long). Nonconst iterators involve additional checking, and are hence a bit slower still. (We expect that eventually some common algorithms will be specialized so that this cost is not encountered. Currently only output, conversion to a C string, and the single-character find member function are treated in this way.)
Iterators are on the order of a dozen words in size. This means that copying them, though not tremendously expensive, is not a trivial operation. Avoid postincrementing iterators; use preincrement whenever possible. (The interface also provides primitives for indexing into a string using integer character positions. Passing positions around is clearly much cheaper, but this makes the indexing operation expensive, again roughly logarithmic in the length of the rope.)

Experience with previous implementations for other programming languages suggests that ropes are a good choice as the normal or default representation of strings in a program. It will occasionally be necessary to use some type of character array, such as vector<char>, in places that are particularly sensitive to the performance of traversals or in-place updates. But the use of ropes minimizes the number of cases in which program running times become intolerable due to unexpectedly long string inputs.

A rope is almost, but not quite, a Sequence. It supports random access const_iterators. Forward or backward traversals take constant time per operation. Nonconstant iterators are also provided. However, assignment through a nonconst iterator is an expensive operation (basically logarithmic time, but with a large constant). It should be avoided in frequently executed code.

In order to discourage accidental use of expensive operations, the begin and end member functions on ropes return const_iterator. If non-const iterators are desired, the member functions mutable_begin and mutable_end should be used.

Any modification of a rope invalidates const iterators referring to the rope. Mutable iterators refer to the same position in the same rope after an update. (This may be surprising if the iterators refers to a position after an insertion point.) They remain valid unless the iterator refers to a position that is more than one past the end of the resulting rope.

Definition

Defined in rope.h. Some of implementation is contained in the internal file ropeimpl.h.

Example

crope r(1000000, 'x');          // crope is rope<char>. wrope is rope<wchar_t>
                                // Builds a rope containing a million 'x's.
                                // Takes much less than a MB, since the
                                // different pieces are shared.
crope r2 = r + "abc" + r;       // concatenation; takes on the order of 100s
                                // of machine instructions; fast
crope r3 = r2.substr(1000000, 3);       // yields "abc"; fast.
crope r4 = r2.substr(1000000, 1000000); // also fast.
reverse(r2.mutable_begin(), r2.mutable_end());
                                // correct, but slow; may take a
                                // minute or more.

Template parameters

Parameter	Description	Default
`T`	The `rope`'s value type: usually `char` or `wchar_t`. [2]
`Alloc`	The `rope`'s allocator, used for all internal memory management.	`alloc`

Model of

Random Access Container. Almost, but not quite, a model of Front Insertion Sequence and Back Insertion Sequence.

Type requirements

None, except for those imposed by the requirements of Random Access Container.

Public base classes

None.

Members

Member	Where defined	Description
`value_type`	Container	The `rope`'s value type `T`, usually `char` or `wchar_t`.
`difference_type`	Container	A signed integral type.
`size_type`	Container	An unsigned integral type.
`reference`	Container	Reference to a `rope` element. [3]
`const_reference`	Container	Const reference to `T`. [3]
`pointer`	Container	Pointer to `T`. [3]
`const_pointer`	Container	Const pointer to `T`. [3]
`const_reverse_iterator`	Reversible Container	Const iterator used to iterate backwards through a `rope`.
`reverse_iterator`	Reversible Container	Mutable iterator used to iterate backwards through a `rope`.
`iterator`	Container	Mutable random access iterator used to iterate through a `rope`.
`const_iterator`	Container	Const random access iterator used to iterate through a `rope`.
`rope(const charT* s)`	`rope`.	Constructs a `rope` from a C string.
`rope(const charT* s, size_t n)`	`rope`.	Constructs a `rope` from a (not necessarily null-terminated) array of `charT`.
`rope(const const_iterator& f, const const_iterator& l)`	Sequence	Creates a `rope` with a copy of a range.
`rope(const iterator& f, const iterator& l)`	Sequence	Creates a `rope` with a copy of a range.
`rope(const charT* f, const charT* l)`	Sequence	Creates a `rope` with a copy of a range.
`rope(charT c)`	`rope`.	Single-character constructor.
`rope()`	Container	Default constructor.
`rope(char_producer<charT>*, size_t, bool)`	`rope`	See below.
`rope(const rope& x)`	Container	The copy constructor.
`~rope()`	Container	The destructor.
`rope& operator=(const rope&x)`	Container	The assignment operator.
`void swap(rope& x)`	Container	Swaps the contents of two `rope`s.
`size_type size() const`	Container	Returns the size of the `rope`.
`size_type length() const`	`rope`	Same as `size`
`size_type max_size() const`	Container	Size of longest `rope` guaranteed to be representable.
`bool empty() const`	Container	Equivalent to `size() == 0`.
`const_iterator begin() const`	Container	Returns an `const_iterator` pointing to the beginning of the `rope`.
`const_iterator end() const`	Container	Returns an `const_iterator` pointing to the end of the `rope`.
`iterator mutable_begin()`	`rope`	Returns an `iterator` pointing to the beginning of the `rope`.
`iterator mutable_end()`	`rope`	Returns an `iterator` pointing to the end of the `rope`.
`const_reverse_iterator rbegin() const`	Reversible Container	Returns a `const_reverse_iterator` pointing to the beginning of the reversed `rope`
`const_reverse_iterator rend() const`	Reversible Container	Returns a `const_reverse_iterator` pointing to the end of the reversed `rope`
`iterator mutable_rbegin()`	`rope`	Returns a `reverse_iterator` pointing to the beginning of the reversed `rope`.
`iterator mutable_rend()`	`rope`	Returns a `reverse_iterator` pointing to the end of the reversed `rope`.
`charT operator[](size_type n) const`	Random Access Container	Returns the `n`'th element.
`charT at(size_type pos) const`	Random Access Container	Returns the `n`'th element.
`reference mutable_reference_at(size_type n)`	`rope`	Returns a `reference` to the `n`th element.
`int compare(const rope&) const`	`rope`.	Three-way comparison. See below.
`charT front() const`	Sequence	Returns the first element.
`charT back() const`	Back Insertion Sequence	Returns the last element.
`void push_front()`	Front Insertion Sequence	Inserts a new element at the front.
`void push_back(charT)`	Back Insertion Sequence	Inserts a new element at the end.
`void pop_front()`	Front Insertion Sequence	Removes the first element.
`void pop_back()`	Back Insertion Sequence	Removes the last element.
`iterator insert(const iterator& p, const rope& x)`	`rope`	Inserts the contents of `x` before `p`.
`iterator insert(const iterator& p, charT c)`	Sequence	Inserts `c` before `p`.
`iterator insert(const iterator& p)`	Sequence	Inserts `charT()` before `p`.
`iterator insert(const iterator& p, size_t n, charT c)`	Sequence	Inserts `n` copies of `c` before `p`.
`iterator insert(const iterator& p, const charT* s)`	`rope`	Inserts a C string before `p`.
`iterator insert(const iterator& p, const charT* s, size_t n)`	`rope`	Inserts a (not necessarily null-terminated) array of `charT` before `p`.
`iterator insert(const iterator& p, const charT* f, const char* l)`	Sequence	Inserts the range `[f, l)` before `p`.
iterator insert(const iterator& p, const const_iterator& f, const const_iterator& l)	Sequence	Inserts the range `[f, l)` before `p`.
iterator insert(const iterator& p, const iterator& f, const iterator& l)	Sequence	Inserts the range `[f, l)` before `p`.
`void insert(size_t i, const rope& x)`	`rope`	Inserts the contents of `x` before the `i`th element.
`void insert(size_t i, charT c)`	`rope`	Inserts the character `c` before the `i`th element.
`void insert(size_t i)`	`rope`	Inserts the character `charT()` before the `i`th element.
`void insert(size_t i, size_t n, charT c)`	`rope`	Inserts `n` copies of `c` before the `i`th element.
`void insert(size_t i, const charT* s)`	`rope`	Inserts a C string before the `i`th element.
`void insert(size_t i, const charT* s, size_t n)`	`rope`	Inserts a (not necessarily null-terminated) array of `charT` before the `i`th element.
`void insert(size_t i, const charT* f, const charT* l)`	`rope`	Inserts the range `[f, l)` before the `i`th element.
void insert(size_t i, const const_iterator& f, const const_iterator& l)	`rope`	Inserts the range `[f, l)` before the `i`th element.
void insert(size_t i, const iterator& f, const iterator& l)	`rope`	Inserts the range `[f, l)` before the `i`th element.
`void erase(const iterator& p)`	Sequence	Erases the element pointed to by `p`.
`void erase(const iterator& f, const iterator& l)`	Sequence	Erases the range `[f, l)`.
`void erase(size_t i, size_t n)`	`rope`	Erases `n` elements, starting with the `i`th element.
`append(const charT* s)`	`rope`	Appends a C string.
`append(const charT* s, size_t)`	`rope`	Appends a (not necessarily null-terminated) array of `charT`.
`append(const charT* f, const charT* l)`	`rope`	Appends a range.
`append(charT c)`	`rope`	Appends the character `c`.
`append()`	`rope`	Appends the character `charT()`.
`append(size_t n, charT c)`	`rope`	Appends `n` copies of `c`.
`append(const rope& x)`	`rope`	Appends the rope `x`.
`void replace(const iterator& f, const iterator& l, const rope&)`	`rope`	See below.
`void replace(const iterator& f, const iterator& l, charT)`	`rope`	See below.
`void replace(const iterator& f, const iterator& l, const charT* s)`	`rope`	See below.
void replace(const iterator& f, const iterator& l, const charT* s, size_t n)	`rope`	See below.
void replace(const iterator& f1, const iterator& l1, const charT* f2, const charT* l2)	`rope`	See below.
void replace(const iterator& f1, const iterator& l1, const const_iterator& f2, const const_iterator& l2)	`rope`	See below.
void replace(const iterator& f1, const iterator& l1, const iterator& f2, const iterator& l2)	`rope`	See below.
`void replace(const iterator& p, const rope& x)`	`rope`	See below.
`void replace(const iterator& p, charT c)`	`rope`	See below.
`void replace(const iterator& p, const charT* s)`	`rope`	See below.
`void replace(const iterator& p, const charT* s, size_t n)`	`rope`	See below.
void replace(const iterator& p, const charT* f, const charT* l)	`rope`	See below.
void replace(const iterator& p, const_iterator f, const_iterator l)	`rope`	See below.
void replace(const iterator& p, iterator f, iterator l)	`rope`	See below.
`void replace(size_t i, size_t n, const rope& x)`	`rope`	See below.
`void replace(size_t i, size_t n, const charT* s, size_t n)`	`rope`	See below.
`void replace(size_t i, size_t n, charT c)`	`rope`	See below.
`void replace(size_t i, size_t n, const charT* s)`	`rope`	See below.
void replace(size_t i, size_t n, const charT* f, const charT* l)	`rope`	See below.
void replace(size_t i, size_t n, const const_iterator& f, const const_iterator& l)	`rope`	See below.
void replace(size_t i, size_t n, const iterator& f, const iterator& l)	`rope`	See below.
`void replace(size_t i, charT c)`	`rope`	See below.
`void replace(size_t i, const rope& x)`	`rope`	See below.
`void replace(size_t i, const charT* s)`	`rope`	See below.
`void replace(size_t i, const charT* s, size_t n)`	`rope`	See below.
`void replace(size_t i, const charT* f, const charT* l)`	`rope`	See below.
void replace(size_t i, const const_iterator& f, const const_iterator& l)	`rope`	See below.
void replace(size_t i, const iterator& f, const iterator& l)	`rope`	See below.
`rope substr(iterator f) const`	`rope`	See below.
`rope substr(const_iterator f) const`	`rope`	See below.
`rope substr(iterator f, iterator l) const`	`rope`	See below.
`rope substr(const_iterator f, const_iterator l) const`	`rope`	See below.
`rope substr(size_t i, size_t n = 1) const`	`rope`	See below.
`void copy(charT* buf) const`	`rope`	Copies a rope into an array of `charT`.
size_type copy(size_type pos, size_type n, charT* buf)	`rope`	Copies a rope into an array of `charT`.
`const charT* c_str() const`	`rope`	See below.
`void delete_c_str()`	`rope`	See below.
`rope operator+(const rope& L, const rope&R)`	`rope`	Concatenates `L` and `R`. This is a global function, not a member function.
`rope& operator+=(rope& L, const rope& R)`	`rope`	Appends `R` to `L`. This is a global function, not a member function.
`rope operator+(const rope& L, const charT* s)`	`rope`	Concatenates `L` and `s`. This is a global function, not a member function.
`rope& operator+=(rope& L, const charT* s)`	`rope`	Appends `s` to `L`. This is a global function, not a member function.
`rope operator+(const rope& L, charT c)`	`rope`	Concatenates `L` and `c`. This is a global function, not a member function.
`rope& operator+=(rope& L, charT c)`	`rope`	Appends `c` to `L`. This is a global function, not a member function.
`bool operator<(const rope&, const rope&)`	Forward Container	Lexicographical comparison. This is a global function, not a member function.
`bool operator==(const rope&, const rope*)`	Forward Container	Tests two `rope`s for equality. This is a global function, not a member function.
`ostream& operator<<(ostream& os, rope x)`	`rope`	Outputs `x` to the stream `os`. This is a global function, not a member function.

New members

These members are not defined in the Random Access Container requirements, but are specific to rope:

Function	Description
`rope(const charT* s)`	Constructs a `rope` from a C string. The rope consists of the sequence of characters starting with `*s` up to, but not including, the first null character.
`rope(const charT* s, size_t n)`	Constructs a `rope` from an array of `charT`. The rope consists of the characters in the range `[s, s + n)`. Note that this range is permitted to contain embedded null characters.
`rope(charT c)`	Constructs a rope consisting of the single character `c`.
`rope(char_producer<charT>* cp, size_t n, bool destroy)`	Constructs a rope of size `n`, whose characters are computed as needed by `cp`. The object `cp` must be valid as long as any reference to the resulting `rope`, or a `rope` derived from it, may be used. If `destroy` is `true`, then `delete cp` will be executed automatically once `cp` is no longer needed. Typically `destroy` will be `true` unless `cp` is a pointer to statically allocated storage. It is rarely safe to allocate `cp` on the stack.
`size_type length() const`	Synonym for `size`
`iterator mutable_begin()`	Returns an `iterator` pointing to the beginning of the `rope`. This member function exists because mutable `rope` iterators are much more expensive than constant `rope` iterators.
`iterator mutable_end()`	Returns an `iterator` pointing to the end of the `rope`. This member function exists because mutable `rope` iterators are much more expensive than constant `rope` iterators.
`iterator mutable_rbegin()`	Returns a `reverse_iterator` pointing to the beginning of the reversed `rope`. This member function exists because mutable `rope` iterators are much more expensive than constant `rope` iterators.
`iterator mutable_rend()`	Returns a `reverse_iterator` pointing to the end of the reversed `rope`. This member function exists because mutable `rope` iterators are much more expensive than constant `rope` iterators.
`reference mutable_reference_at(size_type n)`	Returns a `reference` to the `n`th element. This member function exists because mutable references to `rope` elements have fairly high overhead.
`int compare(const rope& x)`	Three-way comparison, much like the function `strcmp` from the standard C library. Returns a negative number if `this` is lexicographically less than `x`, a positive number if `this` is lexicographically greater than `x`, and zero if neither `rope` is lexicographically less than the other.
`iterator insert(const iterator& p, const rope& x)`	Inserts the contents of the `rope` `x` immediately before the position `p`.
`iterator insert(const iterator& p, const charT* s)`	Inserts a C string immediately before the position `p`. The elements that are inserted are the sequence of characters starting with `*s` and up to, but not including, the first null character.
`iterator insert(const iterator& p, const charT* s, size_t n)`	Inserts an array of `charT`. The elements that are inserted are the range `[s, s + n)`. Note that this range is permitted to contain embedded null characters.
`void insert(size_t i, const rope& x)`	Inserts the contents of the `rope` x immediately before the `i`th element.
`void insert(size_t i, size_t n, charT c)`	Inserts `n` copies of `c` immediately before the `i`th element.
`void insert(size_t i, const charT* s)`	Inserts a C string immediately before the `i`th element. The elements that are inserted are the sequence of characters starting with `*s` and up to, but not including, the first null character.
`void insert(size_t i, const charT* s, size_t n)`	Inserts an array of `charT` immediately before the `i`th element. The elements that are inserted are the range `[s, s + n)`. Note that this range is permitted to contain embedded null characters.
`void insert(size_t i, charT c)`	Inserts the character `c` immediately before the `i`th element.
`void insert(size_t i)`	Inserts the character `charT()` immediately before the `i`th element.
`void insert(size_t i, const charT* f, const charT* l)`	Inserts the range `[f, l)` immediately before the `i`th element.
void insert(size_t i, const const_iterator& f, const const_iterator& l)	Inserts the range `[f, l)` immediately before the `i`th element.
void insert(size_t i, const iterator& f, const iterator& l)	Inserts the range `[f, l)` immediately before the `i`th element.
`void erase(size_t i, size_t n)`	Erases `n` elements, starting with the `i`th element.
`append(const charT* s)`	Adds a C string to the end of the `rope`. The elements that are inserted are the sequence of characters starting with `*s` and up to, but not including, the first null character.
`append(const charT* s, size_ nt)`	Adds an array of `charT` to the end of the `rope`. The elements that are inserted are the range `[s, s + n)`. Note that this range is permitted to contain embedded null characters.
`append(const charT* f, const charT* l)`	Adds the elements in the range `[f, l)` to the end of the `rope`.
`append(charT c)`	Adds the character `c` to the end of the `rope`.
`append()`	Adds the character `charT()` to the end of the rope.
`append(const rope& x)`	Adds the contents of the rope `x` to the end of `*this`.
`append(size_t n, charT c)`	Adds `n` copies of `c` to the end of `*this`.
`void replace(const iterator& f, const iterator& l, const rope& x)`	Replaces the elements in the range `[f, l)` with the elements in `x`.
`void replace(const iterator& f, const iterator& l, charT c)`	Replaces the elements in the range `[f, l)` with the single character `c`.
`void replace(const iterator& f, const iterator& l, const charT* s)`	Replaces the elements in the range `[f, l)` with a C string: the sequence of characters beginning with `*s` and up to, but not including, the first null character.
void replace(const iterator& f, const iterator& l, const charT* s, size_t n)	Replaces the elements in the range `[f, l)` with the elements in the range `[s, s + n)`.
void replace(const iterator& f1, const iterator& l1, const charT* f2, const charT* l2)	Replaces the elements in the range `[f1, l1)` with the elements in the range `[f2, l2)`.
void replace(const iterator& f1, const iterator& l1, const const_iterator& f2, const const_iterator& l2)	Replaces the elements in the range `[f1, l1)` with the elements in the range `[f2, l2)`.
void replace(const iterator& f1, const iterator& l1, const iterator& f2, const iterator& l2)	Replaces the elements in the range `[f1, l1)` with the elements in the range `[f2, l2)`.
`void replace(const iterator& p, const rope& x)`	Replaces the element pointed to by `p` with the elements in `x`.
`void replace(const iterator& p, charT c)`	Replaces the element pointed to by `p` with the single character `c`.
`void replace(const iterator& p, const charT* s)`	Replaces the element pointed to by `p` with a C string: the sequence of characters beginning with `*s` and up to, but not including, the first null character.
`void replace(const iterator& p, const charT* s, size_t n)`	Replaces the element pointed to by `p` with the elements in the range `[s, s + n)`.
void replace(const iterator& p, const charT* f, const charT* l)	Replaces the element pointed to by `p` with the elements in the range `[f, l)`.
void replace(const iterator& p, const_iterator f, const_iterator l)	Replaces the element pointed to by `p` with the elements in the range `[f, l)`.
void replace(const iterator& p, iterator f, iterator l)	Replaces the element pointed to by `p` with the elements in the range `[f, l)`.
`void replace(size_t i, size_t n, const rope& x)`	Replaces the `n` elements beginning with the `i`th element with the elements in `x`.
`void replace(size_t i, size_t n, charT c)`	Replaces the `n` elements beginning with the `i`th element with the single character `c`.
`void replace(size_t i, size_t n, const charT* s)`	Replaces the `n` elements beginning with the `i`th element with an array of `charT`: the sequence of characters beginning with `*s` and up to, but not including, the first null character.
`void replace(size_t i, size_t n1, const charT* s, size_t n2)`	Replaces the `n1` elements beginning with the `i`th element with the elements in the range `[s, s + n2)`.
void replace(size_t i, size_t n, const charT* f, const charT* l)	Replaces the `n` elements beginning with the `i`th element with the characters in the range `[f, l)`.
void replace(size_t i, size_t n, const const_iterator& f, const const_iterator& l)	Replaces the `n` elements beginning with the `i`th element with the characters in the range `[f, l)`.
void replace(size_t i, size_t n, const iterator& f, const iterator& l)	Replaces the `n` elements beginning with the `i`th element with the characters in the range `[f, l)`.
`void replace(size_t i, charT c)`	Replaces the `i`th element with the character `c`.
`void replace(size_t i, const rope& x)`	Replaces the `i`th element with elements from the `rope` x.
`void replace(size_t i, const charT* s)`	Replaces the `i`th element with a C string: the sequence of characters beginning with `*s` and up to, but not including, the first null character.
`void replace(size_t i, const charT* s, size_t n)`	Replaces the `i`th element with the elements in the range `[s, s + n)`.
`void replace(size_t i, const charT* f, const charT* l)`	Replaces the `i`th element with the range `[f, l)`.
void replace(size_t i, const const_iterator& f, const const_iterator& l)	Replaces the `i`th element with the range `[f, l)`.
void replace(size_t i, const iterator& f, const iterator& l)	Replaces the `i`th element with the range `[f, l)`.
`rope substr(iterator f) const`	Returns a new `rope` with a single element, `*f`. [4]
`rope substr(const_iterator f) const`	Returns a new `rope` with a single element, `*f`. [4]
`rope substr(iterator f, iterator l) const`	Returns a new `rope` that consists of the range `[f, l)`. [4]
`rope substr(const_iterator f, const_iterator l) const`	Returns a new `rope` that consists of the range `[f, l)`. [4]
`rope substr(size_t i, size_t n = 1) const`	Returns a new `rope` whose elements are the `n` characters starting at the position `i`. [4].
`void copy(charT* buf) const`	Copies the characters in a `rope` into `buf`.
size_type copy(size_type pos, size_type n, charT* buf)	Copies `n` characters, starting at position `pos` in the `rope`, into `buf`. If the `rope` contains fewer than `pos + n` characters, then instead it only copies `size() - pos` characters.
`const charT* c_str() const`	Returns a pointer to a null-terminated sequence of characters that contains all of the characters in a `rope`. [5] [6] The resulting sequence of characters is valid at least as long as the `rope` remains valid and unchanged. Note that the first invocation of this operation on long strings is slow: it is linear in the length of the `rope`.
`void delete_c_str()`	Reclaims the internal storage used by `c_str`. Note that this invalidates the pointer that `c_str` returns.
`rope operator+(const rope& L, const rope& R)`	Returns a new `rope` consisting of the concatenation of `L` and `R`. This is a global function, not a member function.
`rope& operator+=(rope& L, const rope& R)`	Modifies `L` by appending `R`, and returns `L`. This is a global function, not a member function.
`rope operator+(const rope& L, const charT* s)`	Returns a new `rope` consisting of the concatenation of `L` and all of the characters from `s` up to, but not including, the first null character. This is a global function, not a member function.
`rope& operator+=(rope& L, const charT* s)`	Modifies `L` by appending the characters from `s` up to, but not including, the first null character. The return value is `L`. This is a global function, not a member function.
`rope operator+(const rope& L, charT c)`	Returns a new `rope` consisting of `L` with the character `c` appended to it. This is a global function, not a member function.
`rope& operator+=(rope& L, charT c)`	Modifies `L` by appending the character `c`. This is a global function, not a member function.
`ostream& operator<<(ostream& os, rope x)`	Outputs `x` to the stream `os`. This is a global function, not a member function.

Notes

[1] For a detailed discussion of the rope data structure, see H.-J. Boehm, R. Atkinson, and M. Plass, "Ropes: An Alternative to Strings", Software Practice and Experience 25(12):1315, 1995.

[2] Since the value type is usually either char or wchar_t, the library introduces two abbreviations: crope is a typedef for rope<char>, and wrope is a typedef for rope<wchar_t>.

[3] Rope::reference is not value_type&, but a proxy type. In fact, reference is a typedef for the nested class charT_ref_proxy. Const_reference, however, is simply const value_type&. Similarly, const_pointer is just const value_type* but pointer is a proxy type. If r is an object of type reference, then &r is of type pointer.

[4] Note that the return value of substr is conceptually a distinct rope: the two ropes may share storage, but this is a hidden implementation detail. If you modify a rope returned by substr, this will not change the value of the original rope.

[5] The final const qualifier in the member function c_str() is conceptually slightly inaccurate in the interest of conformance to the basic_string interface in the draft C++ standard; the rope is updated to cache the converted string.

[6] Concurrent calls to c_str() are allowed; the cache is updated atomically.