STL中經常使用函數

一、迭代器：把全部與迭代有關的東西全都抽象出來，好比數組的下標、指針、for裏面的、list裏面的、vector裏面的，抽象一下變成了iterator
#include <iostream>
#include <vector>

using namespace std;

int main()
{

vector<int> v;
  for(int i = 0; i < 10; ++i )
 {
     v.push_back(i);
 }
 for(vector<int>::iterator it = v.begin(); it != v.end(); ++it)
 {
     cout << *it << " ";
 }
 cout << endl;
 return 0;

}

二、求和（<numeric> accumulate）

　　accumulate(v.begin(),v.end(),0),把從 v.begin() 開始到 v.end()結束全部的元素加到 0上面去

include <iostream>

include <vector>

include <numeric>

using namespace std;

int main()
{

vector<int> v;
for (int i = 0; i < 10; ++i)
{
    v.push_back(i);
}
for (vector<int>::iterator it = v.begin(); it != v.end(); ++it)
{
    cout << *it << " ";
}
cout << endl;
cout << accumulate(v.begin(), v.end(), 0) << endl;
system("pause");
return 0;

}

三、vector（動態數組）

　vector有內存管理的機制，也就是說對於插入和刪除，vector能夠動態調整所佔用的內存空間。　　

　vector相關函數：begin()/end()/insert()/erase()

include <iostream>

include <vector>

using namespace std;

int main()
{

vector<int> v;
v.push_back(3);  //數組尾部插入3
v.push_back(2);
v.push_back(1);
v.push_back(0);
cout << " 下標 " << v[3] << endl;
cout << " 迭代器 " << endl;
for (vector<int>::iterator i = v.begin(); i != v.end(); ++i)
{
    cout << *i << " ";
}
cout << endl;
//在第一個元素以前插入111  insert begin+n是在第n個元素以前插入
v.insert(v.begin(), 111);
//在最後一個元素以後插入222 insert end + n 是在n個元素以後插入
v.insert(v.end(), 222);

//v.insert(v.end()-1, 666);

for (vector<int>::iterator i = v.begin(); i != v.end(); ++i)
{
    cout << *i << " ";
}
cout << endl;

vector<int> arr(10);
for (int i = 0; i < 10; i++)
{
    arr[i] = i;
}
for (vector<int>::iterator i = arr.begin(); i != arr.end(); ++i)
{
    cout << *i << " ";
}
cout << endl;

//刪除 同insert
arr.erase(arr.begin());

for (vector<int>::iterator i = arr.begin(); i != arr.end(); ++i)
{
    cout << *i << " ";
}
cout << endl;

arr.erase(arr.begin(), arr.begin() + 5);

for (vector<int>::iterator i = arr.begin(); i != arr.end(); ++i)
{
    cout << *i << " ";
}
cout << endl;
system("pause");
return 0;

}

四、數組轉置 (<algorithm> reverse)

　reverse(v.begin(),v.end())

include<iostream>

include<vector>

include<algorithm>

using namespace std;

int main()
{

vector<int> v;
for(int i = 0; i < 10; ++i)
{
    v.push_back(i);
}
for(vector<int>::iterator it = v.begin(); it != v.end(); ++it)
{
    cout << *it << " ";
}
cout << endl;

reverse(v.begin(),v.end());


for(vector<int>::iterator it = v.begin(); it != v.end(); ++it)
{
    cout << *it << " ";
}
cout << endl;
system("pause");
return 0;
}

五、排序（<algorithm> sort）
　　sort(v.begin(),v.end())

include<iostream>

include<vector>

include<algorithm>

using namespace std;

bool Comp(const int &a,const int &b)
{

return a>b;

}

int main()
{

vector<int> v;
v.push_back(1);
v.push_back(3);
v.push_back(2);
v.push_back(55);
v.push_back(-1);
v.push_back(0);
v.push_back(2);
v.push_back(3);
v.push_back(4);

for(vector<int>::iterator it = v.begin(); it != v.end(); ++it)
{
    cout << *it << " ";
}
cout << endl;

//默認升序
sort(v.begin(),v.end());


for(vector<int>::iterator it = v.begin(); it != v.end(); ++it)
{
    cout << *it << " ";
}
cout << endl;

//用降序 須要自定義一個降序函數
sort(v.begin(),v.end(),Comp);


for(vector<int>::iterator it = v.begin(); it != v.end(); ++it)
{
    cout << *it << " ";
}
cout << endl;
system("pause");
return 0;

}

六、刪除

s.erase(it + 1,it + 4); clear（）

#include<iostream>

include<string>

using namespace std;

int main()
{

string s;
s = "0123456789";
cout << s << endl;

string::iterator it = s.begin();

//刪除s[3]
s.erase(it+3);
cout << s << endl;

//刪除s[1]~s[3]
s = "0123456789";
s.erase(it + 1,it + 4);
cout << s << endl;

//所有刪除
s.clear();
cout << "clear : " << s << endl;

return 0;

}

七、查找（find）

　　用find找到string裏面第一個要找到元素（char或者串），找到返回數組下標，找不到返回end（）迭代器。string和vector有不少相同的東西，好比length（），size（），empty（），reverse（），相對也容易，就不一一說了。

八、數字化處理（string）

　　常常會遇到這樣一種狀況，有一個數字，須要把每一位給提取出來，若是用取餘數的方法，花費的時間就會很長，因此能夠當成字符串來處理，方便、省時。

　　例子：求一個整數各位數的和

include<iostream>

include<string>

using namespace std;

int main()
{

string s;
s = "123456789";
int sum = 0;
for(int i = 0; i < s.size(); ++i)
{
    switch(s[i])
    {
        case '1': sum += 1;break;
        case '2': sum += 2;break;
        case '3': sum += 3;break;
        case '4': sum += 4;break;
        case '5': sum += 5;break;
        case '6': sum += 6;break;
        case '7': sum += 7;break;
        case '8': sum += 8;break;
        case '9': sum += 9;break;
    }
}

cout << sum << endl;

return 0;

}

九、string與數值相互轉換( sprintf <sstream> )

include<iostream>

include<string>

include<sstream>

include<cstdio>

using namespace std;
//c++ 方法 把數轉換爲string
string converToString(double x)
{

ostringstream o;
if( o << x)
{
    // str()沒有'\0' c_str有
    return o.str();
}
return "error";
}
double converFromString(const string &s)
{
istringstream i(s);
double x;
if( i >> x)
{
    return x;
}
//if error
return 0.0;
}
int main(){
    char b[100];
    string s1;
    //c語言方法
    sprintf(b,"%d",1987);
    s1 = b;
    cout << s1 << endl;

    string s2 = converToString(1954);
    cout << s2 << endl;

    string s3 = "202";
    int c = converFromString(s3);
    cout << c << endl;

    string s4 = "casacsa6";
    int d = converFromString(s4);
    cout << d << endl;

    string s5 = "21abf4";
    int f = converFromString(s5);
    cout << f << endl;
    return 0;
}

十、正反遍歷，迭代器iterator、reverse_iterator

include<iostream>

include<set>

using namespace std;

int main()
{

set<int> v;
v.insert(1);
v.insert(3);
v.insert(5);
v.insert(2);
v.insert(4);
v.insert(3);

//中序遍歷 升序遍歷
for(set<int>::iterator it = v.begin(); it != v.end(); ++it)
{
    cout << *it << " ";
}
cout << endl;

for(set<int>::reverse_iterator rit = v.rbegin(); rit != v.rend(); ++rit)
{
    cout << *rit << " ";
}
cout << endl;

return 0;

}