Vector uses a class template and needs to be instantiated explicitly.
Single-parameter constructor supports implicit type conversion
Can vector<char> replace string?
The answer is of course no
1. String requires '\0' at the end, which is very compatible with C language.
Vector has no requirements and is not well compatible with C language.
2. The interface of string is richer than that of vector. String has many special interfaces, such as +=, comparing sizes (comparing sizes between vectors is of little significance)
Single-parameter constructor supports implicit type conversion
vector
Alloc: space allocator, memory pool (T improves memory application efficiency)
The following are template parameters
structure
No parameter construction
n T (template) construction vector<int>s(10,1); vector<string>str(10,"***");
An iterator construction is written as a template here, so it is not limited to vector iterator initialization, and iterators of other containers can also be used.
copy construction
void test_vector3()
{
//n个T初始化
vector<int> v1(10, 1);
vector<string> v2(10, "***");
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
for (auto e : v2)
{
cout << e << " ";
}
cout << endl;
// 自己类型的迭代器
vector<int> v3(v1.begin(), v1.end());
for (auto e : v3)
{
cout << e << " ";
}
cout << endl;
//其它类型的迭代器
string str("hello world");
vector<char> v4(str.begin(), str.end());
for (auto e : v4)
{
cout << e << " ";
}
cout << endl;
//指针
int a[] = { 16,2,77,29 };
vector<int> v5(a, a+4);
for (auto e : v5)
{
cout << e << " ";
}
cout << endl;
}
Containers and Algorithms
Algorithm header file
#include<algorithm>
These intervals are generally closed on the left and open on the right.
Access data in a container via iterator
#include<algorithm>
int a[]={16,2,77,29};
vector<int>vint(a,a+4);
//升序
//默认less
sort(vint.begin(),vint.end());
for(auto e:vint)
cout<<e<<" ";
cout<<endl;
//降序
//greater
//greater<int>gt;
//sort(vint.begin(),vint.end(),gt);
//匿名对象
sort(vint.begin(),vint.end(),greater<int>());
for(auto e:vint)
cout<<e<<" ";
cout<<endl;
Reverse iterators can also sort descendingly. It is equivalent to arranging in reverse and traversing backwards.
reserve (open space, do not change size) and resize (open space + initialization, change size)
A common mistake in reserve
This code will report an error and access out of bounds, because the reserve will not change the size.
reserve should be used in conjunction with push_back to insert data
The solution is to use resize to open it
resize will be initialized and the size will also be increased.
void test_vector4()
{
//resize单独使用
vector<int> v1;
//cout << v1.max_size() << endl;
//v1.reserve(10);
v1.resize(10);
for (size_t i = 0; i < 10; i++)
{
v1[i] = i;
}
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
//reserve配合push_back使用
vector<int> v2;
v2.reserve(10);
for (size_t i = 0; i < 10; i++)
{
v2.push_back(i);
}
for (auto e : v2)
{
cout << e << " ";
}
cout << endl;
}
at and []
When at crosses the boundary, an exception is thrown. Throwing an exception is used to record logs.
[] Out-of-bounds is an assertion. The assertion only takes effect in debug and does not work in release.
data is equivalent to c_str in string
push_back和pop_back
tail insertion, tail deletion
Head plug and head deletion are inefficient and do not provide corresponding interfaces.
erase and insert
Delete or insert at any position (can be used for head insertion and head deletion)
If we need to delete certain data, how do we find its location?
vector does not provide a search interface
However, a search interface is provided in the algorithm
The iterator that returns the corresponding position is found, and the next position that returns the last data is not found
void test_vector5()
{
int a[] = { 16,2,77,29,3,33,43,3,2,3,3,2 };
vector<int> v1(a, a + sizeof(a)/sizeof(int));
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
// 头删
v1.erase(v1.begin());
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
// 头插
v1.insert(v1.begin(), 100);
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
// 删除第3个数据
v1.erase(v1.begin()+2);
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
// 删除3，但是不知道3在哪个位置，怎么办？
//vector<int>::iterator pos = find(v1.begin(), v1.end(), 3);
auto pos = find(v1.begin(), v1.end(), 3);
if (pos != v1.end())
{
v1.erase(pos);
}
}
So what do we need to delete all values in the array?
We can delete one and find another, but when we start searching from the next deleted position, it involves the problem of iterator failure and the program crashes directly. Of course, if we start searching again, there will be no such problem, but the efficiency is too low.
void test_vector6()
{
// 删除所有的3 -- 涉及迭代器失效！
while(pos != v1.end())
{
v1.erase(pos);
//pos = find(pos+1, v1.end(), 3);
pos = find(v1.begin(), v1.end(), 3);
}
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
v1.assign(10, 1);
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}
assign
Clear the original data and reassign it
vector expansion logic
g++ uses the sgi version of STL
vs adopts pj version
Full sort
vector OJ question
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