用谓词使用std :: find [英] using std::find with a predicate
问题描述
我想用 std :: find
函数和一个谓词(不确定是否使用正确的单词)。这里是代码
#include< iostream>
#include< vector>
#include< algorithm>
使用namespace std;
class foo {
public:
typedef pair< int,vector< int> >办法;
typedef pair< int,int>指数;
typedef pair< index,vector< way> >条目;
vector<条目>表;
void bar()
{
vector< int> V1;
v1.push_back(1);
v1.push_back(2);
way w = make_pair(1,v1);
vector< way> V2;
v2.push_back(w);
index id = make_pair(10,20);
entry en = make_pair(id,v2);
table.push_back(en);
void insert()
{
index new_id = make_pair(10,20);
if(table.begin(),table.end(),new_id)!= table.end()){
//表中匹配的索引
//然后I将推回一个新的对(方式)
//到条目的第二部分
}
}
};
int main()
{
foo f;
f.bar();
f.insert();
返回0;
code $
正如你所看到的, find() code>应根据每个条目中的第一个元素搜索表
。现在,它表示 ==
不会被重载以比较对
。
解决方案您想 std :: find_if
:
... $ b $如果(find_if(table.begin(),table.end(),[& new_id](const entry& arg){
return arg.first == new_id;})!= ...)
编辑:如果你没有C ++ 11因此不需要lambda表达式),你必须创建一个自定义函子(函数或函数对象)来比较 entry :: first
和搜索到的索引
:
struct index_equal:std :: unary_function< entry,bool>
{
index_equal(const index& idx):idx_(idx){}
bool operator()(const entry& arg)const {return arg.first == idx_; }
const index& idx_;
};
$ b $ ...
if(find_if(table.begin(),table.end(),index_equal(new_id))!= ...)
$ c因为 index
只是一对 int
s,你也可以通过值来捕获它,而不是const引用,以保持代码更清晰,更简洁,但也不重要。
I want to use std::find
function along with a predicate (not sure if I use the correct word). Here is the code
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
class foo {
public:
typedef pair< int, vector<int> > way;
typedef pair< int, int > index;
typedef pair< index, vector<way> > entry;
vector< entry > table;
void bar()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(2);
way w = make_pair( 1, v1 );
vector<way> v2;
v2.push_back(w);
index id = make_pair( 10, 20 );
entry en = make_pair( id, v2 );
table.push_back( en );
}
void insert()
{
index new_id = make_pair( 10, 20 );
if ( find(table.begin(), table.end(), new_id) != table.end() ) {
// index matched in the table
// then I will push back a new pair (way)
// to the second part of the entry
}
}
};
int main()
{
foo f;
f.bar();
f.insert();
return 0;
}
As you can see, find()
should search the table
based on the first element in each entry. Right now, it says that ==
is not overloaded to compare a pair
.
解决方案 You want std::find_if
:
...
if(find_if(table.begin(), table.end(), [&new_id](const entry &arg) {
return arg.first == new_id; }) != ...)
EDIT: If you don't have C++11 (and therefore no lambdas), you have to create a custom functor (function or function object) to do the comparison of entry::first
with the searched index
:
struct index_equal : std::unary_function<entry,bool>
{
index_equal(const index &idx) : idx_(idx) {}
bool operator()(const entry &arg) const { return arg.first == idx_; }
const index &idx_;
};
...
if(find_if(table.begin(), table.end(), index_equal(new_id)) != ...)
EDIT: Since an index
is just a pair of int
s, you may also just capture it by value than const reference, to keep the code clearer and more concise, but it doesn't really matter either.
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