c++关于multiset的头文件包含问题
c++关于multiset的头文件包含问题
ccf19881030
发布于 2019-12-10 17:48:24
发布于 2019-12-10 17:48:24
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最近在Bilibili上看到不少侯捷老师C++的视频教程，侯捷老师翻译了很多C++的经典书籍，比如《Essential C++中文版》、《STL源码剖析》，也写了《深入浅出MFC 第二版》。
使用到multiset这个关联容器时，本来以为Visual Studio2017中会提供#include 这个头文件，没想到加入到显示错误，后来查了下资料，说是multiset只是set的一个特例而已，只需要包含set的头文件即可，使用#include即可。
测试代码如下：
// test_multiset.hpp
#ifndef _TEST_MULTISET_H
#define _TEST_MULTISET_H
#include <set> // 注意：此处不能使用#include <multiset>
#include <stdexcept>
#include <string>
#include <iostream>
#include <ctime>
#include <cstdio> // snprintf()
#include <cstdlib> // abort()
#include <algorithm>
#include "pub.h"
using std::multiset;
using std::cin;
using std::cout;
using std::endl;
using std::string;
using std::exception;
using std::find;
using std::sort;
namespace jj06
{
void test_multiset(long& totalCount)
{
cout << "\ntest_multiset()......... \n";
multiset<string> c;
char buf[10];
clock_t timeStart = clock();
for (long i = 0; i < totalCount; ++i)
{
try {
snprintf(buf, 10, "%d", rand() % 65535);
c.insert(string(buf));
}
catch (std::exception& e) {
cout << "i=" << i << e.what() << endl;
abort();
}
}
cout << "milli-seconds:" << (clock() - timeStart) << endl;
cout << "multiset.size()= " << c.size() << endl;
cout << "multiset.max_size()= " << c.max_size() << endl;
string target = get_a_target_string();
{
timeStart = clock();
auto pItem = ::find(c.begin(), c.end(), target); // 比c.find(...)慢很多
cout << "::find(), mill-seconds: " << (clock() - timeStart) << endl;
if (pItem != c.end())
cout << "found, " << *pItem << endl;
else
cout << "not found! " << endl;
}
{
timeStart = clock();
auto pItem = c.find(target); // 比::find(...)快很多
cout << "::find(), mill-seconds: " << (clock() - timeStart) << endl;
if (pItem != c.end())
cout << "found, " << *pItem << endl;
else
cout << "not found! " << endl;
}
}
}
#endif// pub.h
#ifndef _PUB_H_
#define _PUB_H_
#ifdef _MSC_VER
#define snprintf _snprintf
#endif
#include <string>
#include <cstdio>
#include <iostream>
using std::string;
using std::cin;
using std::cout;
//const long ASIZE = 1000000;
const long ASIZE = 50000;
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, "%d", 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// main.cpp
#include "test_multiset.hpp"
int main(int argc, char* argv[])
{
long totalCount;
cout << "how many elements:";
cin >> totalCount;
srand((unsigned)time(NULL));
jj06::test_multiset(totalCount);
getchar();
return 0;
}运行示例
[root@192 src]# g++ -o test_multiset main.cpp pub.h test_multiset.hpp
[root@192 src]# ./test_multiset
how many elements:1000000
test_multiset().........
milli-seconds:9750000
multiset.size()= 1000000
multiset.max_size()= 461168601842738790
target (0~2147483647): 23456
::find(), mill-seconds: 50000
found, 23456
c.find(), mill-seconds: 0
found, 23456
[root@192 src]# 完整的代码见本人的Github：stl_container_test
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原始发表：2019-12-08 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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