四、C++语言进阶:Boost入门

编程入门 行业动态 更新时间:2024-10-08 01:22:44

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四、C++语言进阶:Boost入门

4 Boost入门

4.1 简介

Boost库是一个可移植、提供源代码的C++库,作为标准库的后备,是C++标准化进程的开发引擎之一,是为C++语言标准库提供扩展的一些C++程序库的总称。

4.2 使用

4.2.1 lamdba表达式

lambda库通过创建一个匿名的lambda表达式来代替实名的函数对象

  • HelloWorld.cpp
#include <iostream>  
#include <boost/lambda/lambda.hpp> 
using namespace boost::lambda; 
using namespace std; 
int main() {(cout << _1 << " " << _2)("Hello","World");
}

结果:

[root@localhost 4]# ./a.out 
Hello World[root@localhost 4]# 
  • HelloWorld2.cpp
#include <iostream>  
#include <boost/lambda/lambda.hpp> 
using namespace boost::lambda; 
using namespace std;int main(){  auto func = std::cout << _1 << " " << _2;func("Hello","World");
}
  • for_each.cpp
#include <iostream>  
#include <iterator>  
#include <algorithm>  
#include <vector>  
#include <boost/lambda/lambda.hpp>  
int main()  
{  using namespace boost::lambda;  using namespace std;  int arr[] = {1,2,3,4,5,6};for_each(arr,arr+6, cout << _1 << " " );cout << endl;vector<int> vec(arr,arr+6);for_each(vec.begin(),vec.end(), cout << _1 << " " );cout << endl;
}

结果:

[root@localhost 4]# ./a.out 
1 2 3 4 5 6 
1 2 3 4 5 6

注:如果需要使用_1_2的成员变量。需要使用绑定bind()

#include <iostream>  
#include <string>  
#include <map>  
#include <algorithm>  
#include "boost/lambda/lambda.hpp"  
#include "boost/lambda/bind.hpp"  using namespace boost::lambda; 
using namespace std; 
int main() {  map<int,string> kv;kv[110] = "匪警";kv[119] = "火警";kv[120] = "急救中心";for_each(kv.begin(),kv.end(), cout << bind(&map<int,string>::value_type::first,_1) << '\t' <<  bind(&map<int,string>::value_type::second,_1) << '\n'); 
}

结果:

[root@localhost 4]# ./a.out 
110	匪警
119	火警
120	急救中心

4.2.2 容器中存放任意类型值

#include <iostream>
#include <string>
#include <vector>
#include <iterator>
#include <boost/any.hpp>int main(){using namespace std;using namespace boost;any a1 = 10;any a2 = 1.1f;any a3 = string("abc");any a4 = "abcefg";cout << any_cast<int>(a1) << endl;cout << any_cast<float>(a2) << endl;cout << any_cast<string&>(a3) << endl;cout << any_cast<const char*>(a4) << endl;vector<any> vec2 = {"abcd",123,3.14};cout << any_cast<const char*>(vec2[0]) << endl;cout << any_cast<int>(vec2[1]) << endl;cout << any_cast<double>(vec2[2]) << endl;vector<any> vec;vec.push_back(10);vec.push_back(12.4);vec.push_back(string("string"));char const* c_str = "const char*";vec.push_back(c_str);cout << any_cast<int>(vec[0]) << endl<< any_cast<double>(vec[1]) << endl<< any_cast<string&>(vec[2]) << endl<< any_cast<char const*>(vec[3]) << endl;// copy(vec.begin(),vec.end(),ostream_iterator<any>(cout,","));
}

结果:

10
1.1
abc
abcefg
abcd
123
3.14
10
12.4
string
const char*

注:
any_cast<>中的类型不是原来的类型会抛出异常。
any已经成为C++17的标准库组件。

4.2.3 数据转化

  • 字符串转数字
#include <iostream>
#include <boost/lexical_cast.hpp>
int main(){int i = boost::lexical_cast<int>("100");float f = boost::lexical_cast<float>("2.01");char chars[] = "1234";int n = boost::lexical_cast<int>(chars,strlen(chars));std::cout << i << " " << f << " " << n << std::endl;// f = boost::lexical_cast<int>("2.01"); // 类型不匹配抛异常
}

结果:

[root@localhost 4]# ./a.out 
100 2.01 1234

注:C++11可以使用stoi()stof()

  • 数字转字符串
#include <string>
#include <iostream>
#include <boost/lexical_cast.hpp>
int main(){std::string str1 = boost::lexical_cast<std::string>(100);std::string str2 = boost::lexical_cast<std::string>(2.01);std::cout << str1 << " " << str2 << std::endl;
}

结果:

[root@localhost 4]# ./a.out 
100 2.0099999999999998
  • 多态对象转换
#include <iostream>
#include <boost/cast.hpp>
using namespace std;
class Base{
public:void Func(){cout << "Base" << endl;}virtual ~Base(){}
};
class Derive : public Base{
public:void Func(){cout << "Derive" << endl;}
};
int main(){Base* b = new Derive;boost::polymorphic_cast<Derive*>(b)->Func();
}

结果:

[root@localhost 4]# ./a.out 
Derive

4.2.4指针容器

特点:容器销毁自动释放指针

类型说明
ptr_vector指针向量
ptr_set指针集合
ptr_array指针数组
ptr_multimap指针一对多映射
#include <iostream>
#include <boost/ptr_container/ptr_vector.hpp>
#include <boost/ptr_container/ptr_set.hpp>
using namespace std;
int main(){boost::ptr_vector<int> pvec;for(int i=0;i<10;++i){pvec.push_back(new int(i));}for(auto n:pvec){cout << n << " ";}cout << endl;boost::ptr_set<int> s;for(size_t i=0;i<10;i++){s.insert(new int(i));}for(auto n:s){cout << n << " ";}cout << endl;
}

结果:

[root@localhost 4]# ./a.out 
0 1 2 3 4 5 6 7 8 9 
0 1 2 3 4 5 6 7 8 9 

4.2.5 退出处理

变量离开(正常/异常)作用域,触发处理代码。

#include <iostream>
#include <boost/scope_exit.hpp>
using namespace std;
int main(){{int *a = new int(10);BOOST_SCOPE_EXIT(a){delete a;}BOOST_SCOPE_EXIT_ENDcout << *a << endl;}
}

结果:

[root@localhost 4]# ./a.out 
10

注:不止用在new/delete,也用在fopen()/fclose(),dlopen()/dlclose()等。与析构函数相似的作用。

4.2.6 遍历BOOST_FOREACH

#include <iostream>
#include <boost/foreach.hpp>
using namespace std;
int main(){int arr[] = {1,2,3,4,5};BOOST_FOREACH(int a,arr) cout << a << endl;
}

结果:

[root@localhost 4]# ./a.out 
1
2
3
4
5

4.2.7 函数绑定

全局函数:boost::bind(函数名, 参数1,参数2,...)
成员函数:boost::bind(&类名::方法名,类实例指针,参数1,参数2)

#include <iostream>
#include <algorithm>
#include <boost/bind.hpp>
using namespace std;
bool comp(int a,int b){return a<b;
}
int main(){int arr[] = {1,2,3,4,5};cout << count_if(arr,arr+5,boost::bind(comp,_1,3)) << endl;cout << count_if(arr,arr+5,boost::bind(comp,2,_1)) << endl;
}

结果:

[root@localhost 4]# ./a.out 
2
3

注:bind支持最多九个参数。占位符被命名为 _1,_2, _3, _4, 直至 _9

4.2.8 不可复制类

#include <boost/nocopyable.hpp>class Test:private boost::nocopyable{// ...  
};

C++11禁用拷贝构造函数的两种方法:

  • (1)设置成delete
#include <iostream>
using namespace std;
class Test {
public:Test(){}Test(const Test&) = delete;Test& operator=(const Test&) = delete;
};
int main() {Test t;Test t2 = t;t2 = t;
}

报错:

[root@localhost 4]# g++ Test.cpp
Test.cpp: In function ‘int main()’:
Test.cpp:11:15: error: use of deleted function ‘Test::Test(const Test&)’Test t2 = t;^
Test.cpp:6:5: note: declared hereTest(const Test&) = delete;^~~~
Test.cpp:12:10: error: use of deleted function ‘Test& Test::operator=(const Test&)’t2 = t;^
Test.cpp:7:11: note: declared hereTest& operator=(const Test&) = delete;^~~~~~~~
  • (2)设置成private:
#include <iostream>
using namespace std;
class Test {
public:Test(){}
private:Test(const Test&) {}Test& operator=(const Test&) {return *this;};
};
int main() {Test t;Test t2 = t;t2 = t;
}

报错:

[root@localhost 4]# g++ Test.cpp
Test.cpp: In function ‘int main()’:
Test.cpp:14:15: error: ‘Test::Test(const Test&)’ is private within this contextTest t2 = t;^
Test.cpp:7:5: note: declared private hereTest(const Test&) {}^~~~
Test.cpp:15:10: error: ‘Test& Test::operator=(const Test&)’ is private within this contextt2 = t;^
Test.cpp:8:11: note: declared private hereTest& operator=(const Test&) {^~~~~~~~

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四、C++语言进阶:Boost入门

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