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Copy pathvector.cpp
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527 lines (434 loc) · 13.8 KB
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/* # vector
*
* Dynamic array: https://en.wikipedia.org/wiki/Dynamic_array
*/
#include "common.hpp"
int main() {
// Create
{
// Empty
{
std::vector<int> v;
// C++11 initializer lists:
std::vector<int> v1{};
assert(v == v1);
}
// Given size
{
std::vector<int> v(3);
assert(v.size() == 3);
}
/* Fill constructor.
*
* Make a `std::vector` with n copies of a single value.
*/
{
// Copies of given object.
{
assert(std::vector<int>(3, 2) == std::vector<int>({2, 2, 2}));
}
// Default constructed objects. int = 0.
{
assert(std::vector<int>(3) == std::vector<int>({0, 0, 0}));
}
}
// Range copy.
{
std::vector<int> v{0, 1, 2};
std::vector<int> v1(v.begin(), v.end());
assert(v == v1);
}
// From existing array.
{
int myints[]{0, 1, 2};
std::vector<int> v(myints, myints + sizeof(myints) / sizeof(int));
std::vector<int> v1 = {0, 1, 2};
assert(v == v1);
}
}
// Vectors have order.
{
std::vector<int> v{0, 1, 2};
std::vector<int> v1{2, 1, 0};
assert(v != v1);
}
/* # Contiguous storage
*
* # Data
*
* Storage is required to be contiguous by TR1:
* http://stackoverflow.com/questions/849168/are-stdvector-elements-guaranteed-to-be-contiguous
*
* C++11 introduces the `data()` method which returns a pointer to the first element.
* It works even if the vector is empty.
* http://stackoverflow.com/questions/6485496/how-to-get-stdvector-pointer-to-the-raw-data
*
* Before C++11, `&v[0]` works for non-empty vectors.
*
* `vector<bool>` as usual is an exception.
*/
{
std::vector<int> v{0, 1, 2};
assert(&v[0] == v.data());
// True because contiguous:
assert(v.data()[1] == v[1]);
}
// size methods
{
/* # size
*
* # length of vector
*
* # size_type
*
* Number of elements in std::vector.
*
* This has type std::vector<X>::size_type
*/
{
std::vector<int> v;
assert(v.size() == 0);
v.push_back(0);
assert(v.size() == 1);
}
/* # resize
*
* If larger than current size, append given element at end.
*
* If smaller than current size, remove elements from end.
*/
{
// Reduce size
{
std::vector<int> v{0, 1};
v.resize(1);
assert((v == std::vector<int>{0}));
}
// Increase size
{
// Using default constructor objects.
{
std::vector<int> v{1};
v.resize(3);
assert((v == std::vector<int>{1, 0, 0}));
}
// Using copies of given object.
{
std::vector<int> v{1};
v.resize(3, 2);
assert((v == std::vector<int>{1, 2, 2}));
}
}
}
}
// Capacity methods.
{
/* # capacity
*
* Get currently allocated size.
*
* Different from size, which is the number of elements in the std::vector!
*
* At least as large as size.
*
* Likely to be a power of 2 on most implementations.
*/
{
std::vector<int> v;
v.push_back(0);
v.push_back(1);
v.push_back(2);
assert(v.capacity() >= 3);
std::cout << "capacity = " << v.capacity() << std::endl;
}
// # max_size: estimative of what your OS allows you to allocate
{
std::cout << "max_size (MiB) = " << std::vector<int>().max_size() / (1 << 20) << std::endl;
}
// # reserve: increase allocated size if larger than current size.
{
std::vector<int> v;
v.reserve(3);
assert(v.capacity() >= 3);
// size() is untouched
assert(v.empty());
}
#if __cplusplus >= 201103L
// # shrink_to_fit
{
std::vector<int> v{0, 1};
v.reserve(4);
v.shrink_to_fit();
assert(v.capacity() == 2);
}
#endif
}
// `std::vector` stores copies of elements, not references.
{
std::string s = "abc";
std::vector<std::string> v{s};
v[0][0] = '0';
assert(v[0] == "0bc");
assert(s == "abc");
}
// Modify.
{
{
std::vector<int> v;
v = {0};
v = {0, 1};
assert((v == std::vector<int>{0, 1}));
}
/*
# push_back
# append
Push to the end of the std::vector.
Amortized time O(1), but may ocassionaly make the std::vector grow,
which may required a full data copy to a new location if the
current backing array cannot grow.
# push_front
Does not exist for std::vector, as it would always be too costly (requires to move
each element forward.) Use deque if you need that.
*/
{
std::vector<int> v;
std::vector<int> v1;
v.push_back(0);
v1 = {0};
assert(v == v1);
v.push_back(1);
v1 = {0, 1};
assert(v == v1);
/*
push_back makes copies with assign `=`
If you want references, use pointers, or even better, auto_ptr.
*/
{
std::vector<std::string> v;
std::string s = "abc";
v.push_back(s);
v[0][0] = '0';
assert(v[0] == "0bc");
//s was not changed
assert(s == "abc");
}
}
/*
# pop_back
Remove last element from std::vector.
No return val. Rationale: http://stackoverflow.com/questions/12600330/pop-back-return-value
*/
{
std::vector<int> v{0, 1};
v.pop_back();
assert(v == std::vector<int>{0});
v.pop_back();
assert(v == std::vector<int>{});
}
/*
# insert
This operation is inneficient for `std::vector` if it is not done at the end.
# concatenate
The range form of insert can be used to append one vector to anoter.
*/
{
// Single element form.
{
std::vector<int> v = {0,1};
std::vector<int> v1;
v.insert(v.begin(), -1);
v1 = {-1, 0, 1};
assert(v == v1);
v.insert(v.end(), 2);
v1 = {-1, 0, 1, 2};
assert(v == v1);
}
// Range form.
{
std::vector<int> v = {0,1};
std::vector<int> v1 = {2,3};
v.insert(v.end(), v1.begin(), v1.end());
assert((v == std::vector<int>{0, 1, 2, 3}));
}
}
/*
# erase
Remove given elements from container given iterators to those elements.
This operation is inneficient for std::vectors,
since it may mean reallocation and therefore up to $O(n)$ operations.
Returns a pointer to the new location of the element next to the last removed element.
*/
{
// Single element
{
std::vector<int> v{0, 1, 2};
auto it = v.erase(v.begin() + 1);
assert((v == std::vector<int>{0, 2}));
assert(*it == 2);
}
// Range
{
std::vector<int> v{0, 1, 2, 3};
auto it = v.erase(v.begin() + 1, v.end() - 1);
assert((v == std::vector<int>{0, 3}));
assert(*it == 3);
}
}
/*
# remove
Helper to remove all elements that compare equal to a value from container.
Does not actually remove the elements: only ensures that the beginning of the range
does not contain the item to be removed.
Ex:
0, 1, 0, 2, 0, 1
Value to remove: `0`
Range to remove from:
0, 1, 0, 2, 0, 1
----------
After the remove:
1, 2, X, Y, 0, 1
----------
where `X` and `Y` are trash, and not necessarily 0!
To actually remove the items, an `erase` is needed after remove
because `remove` is not a class method and thus cannot remove items from a container.
This is called the erase and remove idiom.
After a remove the container becomes:
1, 2, 0, 1
# erase and remove idiom
# remove and erase idiom
See remove.
*/
{
// Verbose version
{
std::vector<int> v{0, 1, 0, 2, 0, 1};
auto end = std::next(v.end(), -2);
auto firstTrashIt = std::remove(v.begin(), end, 0);
// Unpredictable result:
std::cout << "remove:";
for (auto& i : v) std::cout << " " << i;
std::cout << std::endl;
v.erase(firstTrashIt, end);
assert((v == std::vector<int>{1, 2, 0, 1}));
}
// Compact version
{
std::vector<int> v{0, 1, 0, 2, 0, 1};
auto end = std::next(v.end(), -2);
v.erase(std::remove(v.begin(), end, 0), end);
assert((v == std::vector<int>{1, 2, 0, 1}));
}
}
// # remove_if
// # filter
// Algorithm. Remove if a given function evaluates to true on an element.
{
std::vector<int> v{0, 1, 2, 3, 4};
auto end = v.end();
v.erase(std::remove_if(v.begin(), end, odd), end);
assert((v == std::vector<int>{0, 2, 4}));
// Common combo with lambdas
{
std::vector<int> v{0, 1, 2, 3, 4};
auto end = v.end();
v.erase(std::remove_if(v.begin(), end,
[](int i) {return i % 2 == 1;}), end);
assert((v == std::vector<int>{0, 2, 4}));
}
}
// # transform
// Algorithm. Replace elements by output of a function.
{
std::vector<int> v{0, 1, 2};
std::transform(v.begin(), v.end(), v.begin(),
[](int i) {return i * i;});
assert((v == std::vector<int>{0, 1, 4}));
}
// # clear
// Make the vector empty.
{
std::vector<int> v{0, 1, 2};
v.clear();
assert(v.empty());
}
/*
# print vector
# vector to string
No built-in way.
http://stackoverflow.com/questions/4850473/pretty-print-c-stl-containers
190 votes on question, 30 on top answer! Come on C++!
http://stackoverflow.com/questions/1430757/c-vector-to-string?lq=1
*/
// ERROR: no default operator `<<`.
//cout << v;
}
// Random access is O(1) since array backed
{
std::vector<int> v{0, 1, 2};
// First element:
assert(v.front() == 0);
assert(v.front() == v[0]);
// Last element:
assert(v.back() == 2);
// Nth element:
v[0] = 1;
assert(v[0] == 1);
/*
BAD: just like array overflow will not change std::vector size,
and is unlikelly to give an error
*/
{
//v1[2] = 2;
}
/*
# back Get reference to last element in vector.
# front Get reference to first element in vector.
# at Like `[]`, but does bound checking and throws `out_of_range` in case of overflow.
*/
{
std::vector<int> v{0, 1, 2};
assert(v.front() == 0);
assert(v.at(1) == 1);
assert(v.back() == 2);
try {
assert(v.at(3) == 0);
} catch (std::out_of_range& e) {
} catch (...) {
assert(false);
}
/* Undefined on empty. */
{
std::vector<int> v;
//v.front();
//v.back();
}
}
}
/*
# bool std::vector
*bool std::vectors are evil!*
The standard requires `vector` to have an specialization for bool which packs bits efficiently.
While efficient, in order to work this specialization breaks common std::vector interfaces
that require taking addresses only in the case of this specialization, since it does not
make sense to takes addresses anymore.
Alternatives to `vector<bool>`: <http://stackoverflow.com/questions/670308/alternative-to-vectorbool>
A good alternative seem to be deque<bool>, which behaves as intended.
*/
{
// Works fine and dandy as expected.
{
std::vector<int> v{1, 0};
int& i(v[0]);
}
// Does not compile!!!
{
std::vector<bool> v{true, false};
//bool& b(v[0]);
}
// It was not a problem with bool, the problem really is `vector<bool>`.
{
bool b[]{true, false};
bool& b2(b[0]);
}
}
}