[c++] STL = Standard Template Library

How many people give up, because of YOU.

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先实践，最后需要总结。

1. 数据流中的数据按照一定的格式<T>提取 -------> 放在vector中。

2. 注意 vector.begin(), vector.front()的区别。

3. accumulate()求sum。（与valarrary貌似有一拼，孰优孰劣？---- 可能后者效率更高）

4. multiplies<int>()   c++ --> reference --> <functional> --> multiplies

#include<math.h>
#include<iostream>
#include<fstream>
#include<algorithm>
#include<functional>
#include<numeric>
#include<vector>
#include<iterator>

// continue...

int main() {
    std::vector<int> v;
    std::ifstream in("numbers.txt");

    //Jeff -->
    //1. Input stream --> in, 迭代器 迭代出int from stream。
    //2. Call default constructor, generate ‘eof‘.
    //3. Use back_inserter to call Container‘s member function.
    std::copy(std::istream_iterator<int>(in), std::istream_iterator<int>(),
              std::back_inserter(v));

    for (unsigned int i = 0; i < v.size(); i++)
    {
        std::cout << v[i] << std::endl;
    }

    /**************************************************************************/

    //Jeff --> sort on specific range.
    //         begin: return iterator.
    std::sort(v.begin(), v.end());
    //Jeff --> front: return &value.
    std::cout << "min/max: " << v.front() << " " << v.back() << std::endl;

    std::cout << "median: " << *(v.begin() + (v.size()/2)) << std::endl;
    std::cout << "average: " << accumulate(v.begin(), v.end(), 0.0) / v.size() << std::endl;
    std::cout << "geomean: " << std::pow( accumulate(v.begin(), v.end(), 1.0, std::multiplies<double>()), 1.0/v.size() ) << std::endl;
}

字典map(key, value)的使用。

vector获得stream的数据，然后存在map中。

copy()作为输出的技巧：输出到vector中。

int test02(void)
{
    using namespace std;
    std::vector<string> v;
    // map<key, value>
    std::map<string, int> m;

    std::ifstream in("words.txt");
    std::copy(std::istream_iterator<string>(in), std::istream_iterator<string>(),
              std::back_inserter(v));

    // The number of times it occurs in a file.
    for (auto vi = v.begin(); vi != v.end(); ++vi)
++m[*vi];

    for (auto mi = m.begin(); mi != m.end(); ++mi)
        std::cout << mi->first << ": " << mi->second << std::endl;

    return 0;
}

string也是一个contrainer。

copy()作为输入的技巧：拷贝到ostream。

int test03(void)
{
    std::vector<int> v = {1, 3, 5, 4, 3, 2};
    std::string s("string");

    std::sort(v.begin(), v.end());
    std::copy(v.begin(), v.end(),
              std::ostream_iterator<int>(std::cout, ","));
    std::cout << std::endl;

    std::sort(s.begin(), s.end());
    std::copy(s.begin(), s.end(),
              std::ostream_iterator<char>(std::cout, " "));
    std::cout << std::endl;

    return 0;
}

Next: 

In reality, not all operations are supported in all containers,

http://www.cplusplus.com/reference/stl/

需要逐个实践下，为下一节做准备