QVarLengthArray 类 供低级可变长度数组。 更多...
| 头： | #include <QVarLengthArray> |
| CMake: |
find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core) |
| qmake: | QT += core |
| 继承： | QVLABase and QVLAStorage |
注意： 此类的所有函数 可重入 .
| const_iterator | |
| const_pointer | |
| const_reference | |
| const_reverse_iterator | |
| difference_type | |
| iterator | |
| pointer | |
| reference | |
| reverse_iterator | |
| size_type | |
| value_type |
| QVarLengthArray () | |
| QVarLengthArray (qsizetype size ) | |
| QVarLengthArray (qsizetype size , const T & v ) | |
| QVarLengthArray (const QVarLengthArray<T, Prealloc> & other = Prealloc) | |
| QVarLengthArray (QVarLengthArray<T, Prealloc> && other = Prealloc) | |
| QVarLengthArray (std::initializer_list<T> args ) | |
| QVarLengthArray (InputIterator first , InputIterator last ) | |
| ~QVarLengthArray () | |
| void | append (const T & t ) |
| void | append (T && t ) |
| void | append (const T * buf , qsizetype size ) |
| const T & | at (qsizetype i ) const |
| T & | back () |
| const T & | back () const |
| QVarLengthArray::iterator | begin () |
| QVarLengthArray::const_iterator | begin () const |
| qsizetype | capacity () const |
| QVarLengthArray::const_iterator | cbegin () const |
| QVarLengthArray::const_iterator | cend () const |
| void | clear () |
| QVarLengthArray::const_iterator | constBegin () const |
| const T * | constData () const |
| QVarLengthArray::const_iterator | constEnd () const |
| bool | contains (const AT & value ) const |
| qsizetype | count () const |
| QVarLengthArray::const_reverse_iterator | crbegin () const |
| QVarLengthArray::const_reverse_iterator | crend () const |
| T * | data () |
| const T * | data () const |
| QVarLengthArray::iterator | emplace (QVarLengthArray::const_iterator pos , Args &&... args ) |
| T & | emplace_back (Args &&... args ) |
| bool | empty () const |
| QVarLengthArray::iterator | end () |
| QVarLengthArray::const_iterator | end () const |
| QVarLengthArray::iterator | erase (QVarLengthArray::const_iterator pos ) |
| QVarLengthArray::iterator | erase (QVarLengthArray::const_iterator begin , QVarLengthArray::const_iterator end ) |
| T & | first () |
| const T & | first () const |
| T & | front () |
| const T & | front () const |
| qsizetype | indexOf (const AT & value , qsizetype from = 0) const |
| void | insert (qsizetype i , T && value ) |
| void | insert (qsizetype i , const T & value ) |
| void | insert (qsizetype i , qsizetype count , const T & value ) |
| QVarLengthArray::iterator | insert (QVarLengthArray::const_iterator before , qsizetype count , const T & value ) |
| QVarLengthArray::iterator | insert (QVarLengthArray::const_iterator before , T && value ) |
| QVarLengthArray::iterator | insert (QVarLengthArray::const_iterator before , const T & value ) |
| bool | isEmpty () const |
| T & | last () |
| const T & | last () const |
| qsizetype | lastIndexOf (const AT & value , qsizetype from = -1) const |
| qsizetype | length () const |
| void | pop_back () |
| void | push_back (const T & t ) |
| void | push_back (T && t ) |
| QVarLengthArray::reverse_iterator | rbegin () |
| QVarLengthArray::const_reverse_iterator | rbegin () const |
| void | remove (qsizetype i , qsizetype count = 1) |
| qsizetype | removeAll (const AT & t ) |
| qsizetype | removeIf (Predicate pred ) |
| void | removeLast () |
| bool | removeOne (const AT & t ) |
| QVarLengthArray::reverse_iterator | rend () |
| QVarLengthArray::const_reverse_iterator | rend () const |
| void | replace (qsizetype i , const T & value ) |
| void | reserve (qsizetype size ) |
| void | resize (qsizetype size ) |
| void | resize (qsizetype size , const T & v ) |
| void | shrink_to_fit () |
| qsizetype | size () const |
| void | squeeze () |
| T | value (qsizetype i ) const |
| T | value (qsizetype i , const T & defaultValue ) const |
| QVarLengthArray<T, Prealloc> & | operator+= (const T & value ) |
| QVarLengthArray<T, Prealloc> & | operator+= (T && value ) |
| QVarLengthArray<T, Prealloc> & | operator<< (const T & value ) |
| QVarLengthArray<T, Prealloc> & | operator<< (T && value ) |
| QVarLengthArray<T, Prealloc> & | operator= (const QVarLengthArray<T, Prealloc> & other = Prealloc) |
| QVarLengthArray<T, Prealloc> & | operator= (QVarLengthArray<T, Prealloc> && other = Prealloc) |
| QVarLengthArray<T, Prealloc> & | operator= (std::initializer_list<T> list ) |
| T & | operator[] (qsizetype i ) |
| const T & | operator[] (qsizetype i ) const |
| qsizetype | erase (QVarLengthArray<T, Prealloc> & array = Prealloc, const AT & t ) |
| qsizetype | erase_if (QVarLengthArray<T, Prealloc> & array = Prealloc, Predicate pred ) |
| size_t | qHash (const QVarLengthArray<T, Prealloc> & key = Prealloc, size_t seed = 0) |
| bool | operator!= (const QVarLengthArray<T, Prealloc1> & left = Prealloc1, const QVarLengthArray<T, Prealloc2> & right = Prealloc2) |
| bool | operator< (const QVarLengthArray<T, Prealloc1> & lhs = Prealloc1, const QVarLengthArray<T, Prealloc2> & rhs = Prealloc2) |
| bool | operator<= (const QVarLengthArray<T, Prealloc1> & lhs = Prealloc1, const QVarLengthArray<T, Prealloc2> & rhs = Prealloc2) |
| bool | operator== (const QVarLengthArray<T, Prealloc1> & left = Prealloc1, const QVarLengthArray<T, Prealloc2> & right = Prealloc2) |
| bool | operator> (const QVarLengthArray<T, Prealloc1> & lhs = Prealloc1, const QVarLengthArray<T, Prealloc2> & rhs = Prealloc2) |
| bool | operator>= (const QVarLengthArray<T, Prealloc1> & lhs = Prealloc1, const QVarLengthArray<T, Prealloc2> & rhs = Prealloc2) |
The C++ language doesn't support variable-length arrays on the stack. For example, the following code won't compile:
int myfunc(int n) { int table[n + 1]; // WRONG ... return table[n]; }
The alternative is to allocate the array on the heap (with
new
):
int myfunc(int n) { int *table = new int[n + 1]; ... int ret = table[n]; delete[] table; return ret; }
However, if myfunc() is called very frequently from the application's inner loop, heap allocation can be a major source of slowdown.
QVarLengthArray is an attempt to work around this gap in the C++ language. It allocates a certain number of elements on the stack, and if you resize the array to a larger size, it automatically uses the heap instead. Stack allocation has the advantage that it is much faster than heap allocation.
范例：
int myfunc(int n) { QVarLengthArray<int, 1024> array(n + 1); ... return array[n]; }
In the example above, QVarLengthArray will preallocate 1024 elements on the stack and use them unless
n + 1
is greater than 1024. If you omit the second template argument, QVarLengthArray's default of 256 is used.
QVarLengthArry 的值类型必须是 可赋值数据类型 . This covers most data types that are commonly used, but the compiler won't let you, for example, store a QWidget 作为值；取而代之，存储 QWidget *.
QVarLengthArray，像 QList , provides a resizable array data structure. The main differences between the two classes are:
In summary, QVarLengthArray is a low-level optimization class that only makes sense in very specific cases. It is used a few places inside Qt and was added to Qt's public API for the convenience of advanced users.
另请参阅 QList .
[alias]
QVarLengthArray::
const_iterator
Typedef for const T *. Provided for STL compatibility.
[alias]
QVarLengthArray::
const_pointer
Typedef for const T *. Provided for STL compatibility.
[alias]
QVarLengthArray::
const_reference
Typedef for const T &. Provided for STL compatibility.
[alias]
QVarLengthArray::
const_reverse_iterator
typedef 对于
std::reverse_iterator<const T*>
. Provided for STL compatibility.
[alias]
QVarLengthArray::
difference_type
typedef 对于 ptrdiff_t。为兼容 STL 提供。
[alias]
QVarLengthArray::
iterator
Typedef for T *. Provided for STL compatibility.
[alias]
QVarLengthArray::
pointer
Typedef for T *. Provided for STL compatibility.
[alias]
QVarLengthArray::
reference
Typedef for T &. Provided for STL compatibility.
[alias]
QVarLengthArray::
reverse_iterator
typedef 对于
std::reverse_iterator<T*>
. Provided for STL compatibility.
[alias]
QVarLengthArray::
size_type
typedef 对于 int。为兼容 STL 提供。
[alias]
QVarLengthArray::
value_type
typedef 对于 T。为兼容 STL 提供。
插入 value at index position i in the array. If i is 0, the value is prepended to the vector. If i is size (), the value is appended to the vector.
For large arrays, this operation can be slow ( 线性时间 ), because it requires moving all the items at indexes i and above by one position further in memory. If you want a container class that provides a fast insert () function, use std::list instead.
另请参阅 remove ().
这是重载函数。
插入 value in front of the item pointed to by the iterator before . Returns an iterator pointing at the inserted item.
Constructs an array with an initial size of zero.
[explicit]
QVarLengthArray::
QVarLengthArray
(
qsizetype
size
)
Constructs an array with an initial size of size 元素。
If the value type is a primitive type (e.g., char, int, float) or a pointer type (e.g., QWidget *), the elements are not initialized. For other types, the elements are initialized with a 默认构造值 .
[explicit, since 6.4]
QVarLengthArray::
QVarLengthArray
(
qsizetype
size
, const
T
&
v
)
Constructs an array with an initial size of size elements filled with copies of v .
注意：
This constructor is only available when
T
is copy-constructible.
该函数在 Qt 6.4 引入。
构造副本为 other .
[since 6.0]
QVarLengthArray::
QVarLengthArray
(
QVarLengthArray
<
T
,
Prealloc
> &&
other
= Prealloc)
Move-constructs this variable-length array from other . After the move, other is empty.
该函数在 Qt 6.0 引入。
Constructs an array from the std::initializer_list given by args .
This constructor is only enabled if the compiler supports C++11 initializer lists.
Constructs an array with the contents in the iterator range [ first , last ).
The value type of
InputIterator
must be convertible to
T
.
Destroys the array.
Appends item t to the array, extending the array if necessary.
另请参阅 removeLast ().
This function overloads append.
注意：
Unlike the lvalue overload of append(), passing a reference to an object that is already an element of
*this
leads to undefined behavior:
vla.append(std::move(vla[0])); // BUG: passing an object that is already in the container
追加 size amount of items referenced by buf 到此数组。
Returns a reference to the item at index position i .
i must be a valid index position in the array (i.e., 0 <= i < size ()).
另请参阅 value () 和 operator[] ().
如同 last (). Provided for STL-compatibility.
这是重载函数。
返回 STL 样式迭代器 pointing to the first item in the array.
另请参阅 constBegin () 和 end ().
这是重载函数。
Returns the maximum number of elements that can be stored in the array without forcing a reallocation.
The sole purpose of this function is to provide a means of fine tuning QVarLengthArray 's memory usage. In general, you will rarely ever need to call this function. If you want to know how many items are in the array, call size ().
返回常量 STL 样式迭代器 pointing to the first item in the array.
返回常量 STL 样式迭代器 pointing to the imaginary item after the last item in the array.
Removes all the elements from the array.
Same as resize(0).
返回常量 STL 样式迭代器 pointing to the first item in the array.
Returns a const pointer to the data stored in the array. The pointer can be used to access the items in the array. The pointer remains valid as long as the array isn't reallocated.
This function is mostly useful to pass an array to a function that accepts a plain C++ array.
另请参阅 data () 和 operator[] ().
返回常量 STL 样式迭代器 pointing to the imaginary item after the last item in the array.
另请参阅 constBegin () 和 end ().
返回
true
if the array contains an occurrence of
value
；否则返回
false
.
This function requires the value type to have an implementation of
operator==()
.
另请参阅 indexOf () 和 lastIndexOf ().
如同 size ().
返回常量 STL-style reverse iterator pointing to the first item in the variable length array, in reverse order.
另请参阅 begin (), rbegin ()，和 rend ().
返回常量 STL-style reverse iterator pointing to one past the last item in the variable length array, in reverse order.
另请参阅 end (), rend ()，和 rbegin ().
Returns a pointer to the data stored in the array. The pointer can be used to access and modify the items in the array.
范例：
QVarLengthArray<int> array(10); int *data = array.data(); for (int i = 0; i < 10; ++i) data[i] = 2 * i;
The pointer remains valid as long as the array isn't reallocated.
This function is mostly useful to pass an array to a function that accepts a plain C++ array.
另请参阅 constData () 和 operator[] ().
这是重载函数。
[since 6.3]
template <typename Args>
QVarLengthArray::iterator
QVarLengthArray::
emplace
(
QVarLengthArray::const_iterator
pos
,
Args
&&...
args
)
Inserts an item in front of the item pointed to by the iterator pos , passing args to its constructor.
Returns an iterator pointing at the emplaced item.
该函数在 Qt 6.3 引入。
[since 6.3]
template <typename Args>
T
&QVarLengthArray::
emplace_back
(
Args
&&...
args
)
Inserts an item at the back of this QVarLengthArray , passing args to its constructor.
Returns a reference to the emplaced item.
该函数在 Qt 6.3 引入。
返回
true
if the array has size 0; otherwise returns
false
.
如同 isEmpty (). Provided for STL-compatibility.
返回 STL 样式迭代器 pointing to the imaginary item after the last item in the array.
这是重载函数。
Removes the item pointed to by the iterator pos from the vector, and returns an iterator to the next item in the vector (which may be end ()).
这是重载函数。
Removes all the items from begin up to (but not including) end . Returns an iterator to the same item that end referred to before the call.
Returns a reference to the first item in the array. The array must not be empty. If the array can be empty, check isEmpty () before calling this function.
这是重载函数。
如同 first (). Provided for STL-compatibility.
这是重载函数。
Returns the index position of the first occurrence of value in the array, searching forward from index position from . Returns -1 if no item matched.
This function requires the value type to have an implementation of
operator==()
.
另请参阅 lastIndexOf () 和 contains ().
这是重载函数。
插入 count 个副本对于 value at index position i in the vector.
插入 count 个副本对于 value in front of the item pointed to by the iterator before . Returns an iterator pointing at the first of the inserted items.
返回
true
if the array has size 0; otherwise returns
false
.
Returns a reference to the last item in the array. The array must not be empty. If the array can be empty, check isEmpty () before calling this function.
这是重载函数。
Returns the index position of the last occurrence of the value value in the array, searching backward from index position from 。若 from is -1 (the default), the search starts at the last item. Returns -1 if no item matched.
This function requires the value type to have an implementation of
operator==()
.
另请参阅 indexOf () 和 contains ().
如同 size ().
如同 removeLast (). Provided for STL-compatibility.
Appends item t to the array, extending the array if necessary. Provided for STL-compatibility.
This function overloads push_back.
注意：
Unlike the lvalue overload of push_back(), passing a reference to an object that is already an element of
*this
leads to undefined behavior:
vla.push_back(std::move(vla[0])); // BUG: passing an object that is already in the container
返回 STL-style reverse iterator pointing to the first item in the variable length array, in reverse order.
另请参阅 begin (), crbegin ()，和 rend ().
这是重载函数。
这是重载函数。
移除 count elements from the middle of the array, starting at index position i .
[since 6.1]
template <typename AT>
qsizetype
QVarLengthArray::
removeAll
(const
AT
&
t
)
Removes all elements that compare equal to t from the array. Returns the number of elements removed, if any.
该函数在 Qt 6.1 引入。
另请参阅 removeOne ().
[since 6.1]
template <typename Predicate>
qsizetype
QVarLengthArray::
removeIf
(
Predicate
pred
)
Removes all elements for which the predicate pred returns true from the array. Returns the number of elements removed, if any.
该函数在 Qt 6.1 引入。
另请参阅 removeAll ().
Decreases the size of the array by one. The allocated size is not changed.
另请参阅 append ().
[since 6.1]
template <typename AT>
bool
QVarLengthArray::
removeOne
(const
AT
&
t
)
Removes the first element that compares equal to t from the array. Returns whether an element was, in fact, removed.
该函数在 Qt 6.1 引入。
另请参阅 removeAll ().
返回 STL-style reverse iterator pointing to one past the last item in the variable length array, in reverse order.
另请参阅 end (), crend ()，和 rbegin ().
这是重载函数。
替换项在索引位置 i with value .
i must be a valid index position in the array (i.e., 0 <= i < size ()).
另请参阅 operator[] () 和 remove ().
试图分配内存为至少 size elements. If you know in advance how large the array can get, you can call this function and if you call resize () often, you are likely to get better performance. If size is an underestimate, the worst that will happen is that the QVarLengthArray will be a bit slower.
The sole purpose of this function is to provide a means of fine tuning QVarLengthArray 's memory usage. In general, you will rarely ever need to call this function. If you want to change the size of the array, call resize ().
另请参阅 capacity () 和 squeeze ().
Sets the size of the array to size 。若 size is greater than the current size, elements are added to the end. If size is less than the current size, elements are removed from the end.
If the value type is a primitive type (e.g., char, int, float) or a pointer type (e.g., QWidget *), new elements are not initialized. For other types, the elements are initialized with a 默认构造值 .
[since 6.4]
void
QVarLengthArray::
resize
(
qsizetype
size
, const
T
&
v
)
Sets the size of the array to size 。若 size is greater than the current size, copies of v are added to the end. If size is less than the current size, elements are removed from the end.
注意：
This function is only available when
T
is copy-constructible.
该函数在 Qt 6.4 引入。
如同 squeeze (). Provided for STL-compatibility.
Returns the number of elements in the array.
Releases any memory not required to store the items. If the container can fit its storage on the stack allocation, it will free the heap allocation and copy the elements back to the stack.
The sole purpose of this function is to provide a means of fine tuning QVarLengthArray 's memory usage. In general, you will rarely ever need to call this function.
另请参阅 reserve (), capacity ()，和 resize ().
Returns the value at index position i .
If the index i is out of bounds, the function returns a 默认构造值 . If you are certain that i is within bounds, you can use at () instead, which is slightly faster.
另请参阅 at () 和 operator[] ().
这是重载函数。
If the index i is out of bounds, the function returns defaultValue .
追加 value to the array and returns a reference to this vector.
另请参阅 append () 和 operator<< ().
这是重载函数。
另请参阅 append () 和 operator<< ().
追加 value to the array and returns a reference to this vector.
另请参阅 append () 和 operator+= ().
这是重载函数。
另请参阅 append () 和 operator+= ().
赋值 other to this array and returns a reference to this array.
[since 6.0]
QVarLengthArray
<
T
,
Prealloc
> &QVarLengthArray::
operator=
(
QVarLengthArray
<
T
,
Prealloc
> &&
other
= Prealloc)
移动赋值 other to this array and returns a reference to this array. After the move, other is empty.
该函数在 Qt 6.0 引入。
Assigns the values of list to this array, and returns a reference to this array.
This constructor is only enabled if the compiler supports C++11 initializer lists.
Returns a reference to the item at index position i .
i must be a valid index position in the array (i.e., 0 <= i < size ()).
这是重载函数。
[since 6.1]
template <typename T, qsizetype Prealloc, typename AT>
qsizetype
erase
(
QVarLengthArray
<
T
,
Prealloc
> &
array
= Prealloc, const
AT
&
t
)
Removes all elements that compare equal to t from the array array . Returns the number of elements removed, if any.
注意： t is not allowed to be a reference to an element inside array . If you cannot be sure that this is not the case, take a copy of t and call this function with the copy.
该函数在 Qt 6.1 引入。
另请参阅 erase_if ().
[since 6.1]
template <typename T, qsizetype Prealloc, typename Predicate>
qsizetype
erase_if
(
QVarLengthArray
<
T
,
Prealloc
> &
array
= Prealloc,
Predicate
pred
)
Removes all elements for which the predicate pred returns true from the list array . Returns the number of elements removed, if any.
该函数在 Qt 6.1 引入。
另请参阅 erase ().
返回哈希值为 key ，使用 seed 做计算种子。
返回
true
if the two arrays, specified by
left
and
right
, are
not
equal.
Two arrays are considered equal if they contain the same values in the same order.
This function requires the value type to have an implementation of
operator==()
.
另请参阅 operator== ().
返回
true
if variable length array
lhs
is
lexicographically less than
rhs
；否则返回
false
.
This function requires the value type to have an implementation of
operator<()
.
返回
true
if variable length array
lhs
is
lexicographically less than or equal to
rhs
；否则返回
false
.
This function requires the value type to have an implementation of
operator<()
.
返回
true
if the two arrays, specified by
left
and
right
, are equal.
Two arrays are considered equal if they contain the same values in the same order.
This function requires the value type to have an implementation of
operator==()
.
另请参阅 operator!= ().
返回
true
if variable length array
lhs
is
lexicographically greater than
rhs
；否则返回
false
.
This function requires the value type to have an implementation of
operator<()
.
返回
true
if variable length array
lhs
is
lexicographically greater than or equal to
rhs
；否则返回
false
.
This function requires the value type to have an implementation of
operator<()
.