[C/C++]_[初级]_[使用remove,remove_if,remove_copy_if过滤元素或字符]

场景

我们经常会过滤掉一个容器里不符合的元素,留下有用的元素. 如果用C++98的写法的话必然得用一个for循环+容器的erase的方法进行匹配,代码量也是挺高的,而且erase方法也有自身的注意事项. 而使用 algorithm 库里的remove,remove_if函数能极大的精简代码.

对于在界面里添加的简单搜索框, 搜索特定元素时,也可以使用remove_copy_if来提取这些元素,方便简洁.

例子

#include <iostream>
#include <algorithm>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <assert.h>
#include <ctype.h>
#include <vector>
#include <iterator>

using namespace std;

class A
{

public:
A():valid_(true){}
bool valid_;
int i_;
};

void TestRemove()
{
std::string str = "adfas\nasdf\n\tasdfa\n";
std::cout << "[str:" << str << "]"<< std::endl;

// std::remove
std::cout << ".............std::remove.........." << std::endl;
std::string str_remove = str;
str_remove.erase(std::remove(str_remove.begin(),str_remove.end(),'\n'),str_remove.end());
std::cout << "[str_remove:" << str_remove << "]"<< std::endl;

// std::remove_if
// 移除对象
std::cout << ".............std::remove_if.........." << std::endl;
std::vector<A*> arr_removeif;
for(size_t i = 0; i< 10;++i)
{
A* a = new A();
arr_removeif.push_back(a);
a->i_ = i;
if(i%2) a->valid_ = false;
}

arr_removeif.erase(std::remove_if(arr_removeif.begin(),
arr_removeif.end(),[](A* a)->bool{ return !a->valid_;}),
arr_removeif.end());
for(auto a: arr_removeif)
{
std::cout << a->i_ << std::endl;
assert(!(a->i_ % 2));
}

// 移除字符,可以加 UnaryPredicate 进行过滤.
std::string str_removeif = str;
str_removeif.erase(std::remove_if(str_removeif.begin(),str_removeif.end(),
[](int c)->bool{ return isspace(c & 0xFF);}),
str_removeif.end());
std::cout << "str_removeif: " << str_removeif << std::endl;

// 把需要保留的元素放入另一个容器里,不改变原来的容器.
std::cout << ".............std::remove_copy_if.........." << std::endl;
std::cout << "arr_removeif: " << arr_removeif.size() << std::endl;
std::vector<A*> arr_removecopyif;
std::remove_copy_if(arr_removeif.begin(),
arr_removeif.end(),std::back_inserter(arr_removecopyif ),
[](A* a)->bool{ return !a->valid_;});
std::cout << "arr_removeif: " << arr_removeif.size() << std::endl;
std::cout << "arr_removecopyif: " << arr_removecopyif.size() << std::endl;
//assert(arr_removeif.empty());
for(auto a: arr_removecopyif)
{
std::cout << a->i_ << std::endl;
}
}

int main(int argc, char const *argv[])
{
TestRemove();
return 0;
}

输出:

[str:adfas
asdf
asdfa
]
.............std::remove..........
[str_remove:adfasasdf   asdfa]
.............std::remove_if..........
0
2
4
6
8
str_removeif: adfasasdfasdfa
.............std::remove_copy_if..........
arr_removeif: 5
arr_removeif: 5
arr_removecopyif: 5
0
2
4
6
8

参考

remove-spaces-from-stdstring-in-c

std::remove, std::remove_if

std::remove_copy, std::remove_copy_if