3. 容器的分类与测试 - array

array是一种固定长度的sequence container(顺序容器)

/*
 * @file: container_test.cpp
 */

#include "container.h"

int main(int argc, char **argv)
{
        jj01::test_array();
        return 0;
}

辅助测试方法

/*
 * @file: helper.h
 */
#ifndef __HELPER__
#define __HELPER__
using namespace std;

const long ASIZE = 500000L;

long get_a_target_long()
{
        long target = 0;

        cout << "target (0 ~ " << RAND_MAX << "): ";

        cin >> target;
        return target;
}

string get_a_target_string()
{
        long target = 0;
        char buf[10];

        cout << "target (0 ~ " << RAND_MAX << "): ";
        cin >> target;

        snprintf(buf, 10, "%ld", target);

        return string(buf);
}

int compareLongs(const void *a, const void *b)
{
        return (*(long *)a - *(long *)b);
}

int compareStrings(const void *a, const void *b)
{
        if (*(string *)a > *(string *)b)
                return 1;
        else if (*(string *)a < *(string *)b)
                return -1;
        else
                return 0;
}
#endif

/*
 * @file: container.h
 */
#ifndef _CONTAINER_
#define _CONTAINER_

#include <array>
#include <iostream>
#include <ctime>
#include <cstdlib>   // qsort, bsearch, NULL
#include "helper.h"

namespace jj01
{
void test_array()
{
        cout << "\ntest_array()..........  \n";
        array<long, ASIZE> c;
        clock_t timeStart = clock();

        srand(time(NULL));

        for (long i=0; i<ASIZE; i++)
        {
                c[i] = rand();
        }

        cout << "milli-seconds : " << (clock() - timeStart) << endl;
        cout << "array.size() = " << c.size() << endl;
        cout << "array.front() = " << c.front() << endl;
        cout << "array.back() = " << c.back() << endl;
        cout << "array.data() = " << c.data() << endl;

        long target = get_a_target_long();
        timeStart = clock();
        ::qsort(c.data(), ASIZE, sizeof(long), compareLongs);
        long * pItem = (long *)::bsearch(&target, (c.data()), ASIZE, sizeof(long), compareLongs);
        cout << "qsort() + bsearch(), seconds : " << double(clock() - timeStart) / CLOCKS_PER_SEC << endl;
}
}

#endif

在C++11 C++14 C++98下介输出正常:

pam:~/container_test$ ./container

test_array()..........
milli-seconds : 31713
array.size() = 500000
array.front() = 118519692
array.back() = 2077013023
array.data() = 0x7ffc5c05bee0
target (0 ~ 2147483647): 4535
qsort() + bsearch(), seconds : 0.359465

总结:

标准c库中的排序和查找算法不像C++标准库中那么多, 这里用到了cstdlib中的快速排序库函数qsort()和二分查找bsearch()库函数, 二分查找只有排好序的前提下才能用.

array.data() 取得array的首地址
array.size() 返回array里元素的总个数
array.front() 第一个元素
array.back() 最后一个元素

qsort(c.data(), ASIZE, sizeof(long), compareLongs); 从c.data()地址开始的地方开始, 对ASIZE个空间大小为sizeof(long)的元素按照compareLongs的规则进行排序.

bsearch(&target, (c.data()), ASIZE, sizeof(long), compareLongs) 在按照compareLongs排好序的地址空间查找目标target, 该空间的起始地址为c.data()的个数为ASIZE的大小为sizeof(long)的连续空间.