[英]Using type vector<pair<int,int>>::iterator& in function call
I have written the following piece of test code. 我已经编写了以下测试代码。 The functionality of this code segment is to find the longest continuous sequence from a given set of digits. 该代码段的功能是从给定的一组数字中找到最长的连续序列。 I am using a recursive lambda ( std::function
) implementation in the part of the processing logic related to sorting the vector<pair<int,int>>
. 我在与对vector<pair<int,int>>
进行排序有关的处理逻辑部分中使用了递归lambda( std::function
)实现。
#include <iostream>
#include <vector>
#include <functional>
#include <utility>
#include <string>
using std::vector;
using std::function;
using std::swap;
using std::pair;
using std::make_pair;
using std::string;
using std::cout;
using std::endl;
int main (void){
auto func_obj1 = [&](const string& r, int buffer)->int{
function<void(vector<pair<int,int>>::iterator&, vector<pair<int,int>>::iterator&)> func_obj3 = [&](auto begin, auto end){
if(begin == end){
return;
}
auto tempb = begin;
auto tempe = end - 1;
while(tempb != end){
if((*tempb).second > (*tempe).second){
swap(*tempb, *tempe);
}
}
end = tempe;
func_obj3(begin, end);
};
auto func_obj2 = [&](vector<pair<int,int>>& r)->int{
func_obj3(r.begin(), r.end());
auto iter = r.begin();
auto count = 0;
auto max_count = 0;
while(iter != r.end()){
auto temp = iter + 1;
if((*iter).second + 1 == (*temp).second){
++count;
if(count > max_count){
max_count = count;
}
}
else{
count = 0;
}
++iter;
}
return max_count;
};
vector<pair<int,int>> v;
auto sws = ' ';
auto iter = r.begin();
auto count = 0;
while(iter != r.end()){
if(*iter == sws){
continue;
}
else{
v.push_back(make_pair(count, *iter));
++count;
}
++iter;
}
auto result = func_obj2(v);
return result;
};
string s = "1 9 2 7 3 8 4 ";
auto result = func_obj1(s, s.size());
cout << result << endl;
return 0;
}
The code fails to compile: 该代码无法编译:
g++ -ggdb -std=c++14 -Wall code.cpp
code.cpp:35:5: error: no matching function for call to object of type 'function<void (vector<pair<int, int> >::iterator &, vector<pair<int, int> >::iterator &)>' (aka 'function<void (__wrap_iter<std::__1::pair<int, int> *> &, __wrap_iter<std::__1::pair<int, int> *> &)>')
func_obj3(r.begin(), r.end());
^~~~~~~~~
/Library/Developer/CommandLineTools/usr/include/c++/v1/functional:1677:9: note: candidate function not viable: expects an l-value for 1st argument
_Rp operator()(_ArgTypes...) const;
^
1 error generated.
Can someone advise about how to rectify this? 有人可以建议如何纠正此问题吗?
TIA TIA
Vinod 维诺德
Guess, the error was related to the second line in the compiler output: 猜猜,该错误与编译器输出中的第二行有关:
code.cpp:39:5: error: no matching function for call to object of type 'function<void (vector<pair<int, int> >::iterator &, vector<pair<int, int> >::iterator &)>' (aka 'function<void (__wrap_iter<std::__1::pair<int, int> *> &, __wrap_iter<std::__1::pair<int, int> *> &)>')
func_obj3(r.begin(), r.end());
^~~~~~~~~
/Library/Developer/CommandLineTools/usr/include/c++/v1/functional:1677:9: note: **candidate function not viable: expects an l-value for 1st argument**
_Rp operator()(_ArgTypes...) const;
^
1 error generated.
Changed the invocation arguments to l-values to get rid of the error. 将调用参数更改为l值以消除错误。
based on the error message code.cpp:35:5: error: no matching function for call to object of type 'function<void (vector<pair<int, int> >::iterator &, vector<pair<int, int> >::iterator &)>' (aka 'function<void (__wrap_iter<std::__1::pair<int, int> *> &, __wrap_iter<std::__1::pair<int, int> *> &)>')
基于错误消息code.cpp:35:5: error: no matching function for call to object of type 'function<void (vector<pair<int, int> >::iterator &, vector<pair<int, int> >::iterator &)>' (aka 'function<void (__wrap_iter<std::__1::pair<int, int> *> &, __wrap_iter<std::__1::pair<int, int> *> &)>')
You could try to change the lambda func_obj2 to: 您可以尝试将lambda func_obj2更改为:
auto func_obj2 = [&](vector<pair<int,int>>& r)->int{
using vpitor = std::vector<pair<int,int>>::iterator;
vpitor it_begin = r.begin();
vpitor it_end = r.end();
func_obj3(it_begin, it_end);
...
}
function<void(vector<pair<int,int>>::iterator&, vector<pair<int,int>>::iterator&)>
func_obj3 = /*...*/;
should be 应该
function<void(vector<pair<int,int>>::iterator, vector<pair<int,int>>::iterator&)>
func_obj3 = /*...*/;
Or even should simply be: 甚至应该只是:
auto func_obj3 = [&](auto begin, auto end){/*...*/};
Issue is that in func_obj3(r.begin(), r.end())
, r.begin()
and r.end()
are both rvalues and cannot bind to non-const lvalue references ( vector<pair<int,int>>::iterator&
) that you impose in function signature. 问题是在func_obj3(r.begin(), r.end())
, r.begin()
和r.end()
都是rvalues并且不能绑定到非const lvalue引用( vector<pair<int,int>>::iterator&
),您可以在函数签名中加入。
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