C++ vector - find element, find_if, copy_if

Question

Hello,

it is clear. Struct all is public!

struct PanelData  
{  
	CString Error;  
	CString OrderNo;  
	double SellingPrice;  
  
	map<CString, Component> m_DicProcessdata;  
  
	CString BoardId;  
	bool    PanelReported;  
	  
	vector<subBoard> VecSubBoards;  
	PanelData(CString strBoardId);  
  
	bool operator==(bool a)  
	{  
		return PanelReported == a;  
	}  
};  

https://cplusplus.com/reference/algorithm/find_if
https://cplusplus.com/reference/algorithm/copy_if/

Is predicate, true or false.
How would I have to do it if I say Price less than or equal to 30,34€

For whatever reason is not clear.
When does it make sense?
What would I have to call the call?

https://cplusplus.com/reference/algorithm/find/

The examples only use int, no class, no structure, which is easier.

it9 = find(m_dequePanelData.begin(), m_dequePanelData.end(), [](const PanelData& d) { if (d.Price >= 3) return d; });  
	/*if (it9 != m_dequePanelData.end())  
		std::cout << "Element found in m_dequePanelData: " << *it9->Price << '\n';  
	else  
		std::cout << "Element not found in m_dequePanelData\n";*/  

The third parameter must be the same. I use PanalData as vector now, not bool. Does not work. return value is d from PanelData.

What is the best way to proceed when looking at the transfer parameters?

Answer 1

I haven't followed all of your code and issues, but if your
basic question is how to check a vector of structs to find
an element that meets a condition in one of the struct
members - using std::find_if with a predicate:

// find the first struct in a vector with a double   
// member <= a given value  
  
#include <iostream>     // std::cout  
#include <algorithm>    // std::find_if  
#include <vector>       // std::vector  
#include <iomanip>  
  
struct MyStruct  
{  
    double price;  
};  
  
double threshold = 0.0;  
bool PriceRanges(MyStruct ms)  
{  
    return (ms.price <= threshold);  
}  
  
int main() {      
    std::vector<MyStruct> myvector;  
  
    MyStruct mystruxt;  
       
    mystruxt.price = 35.00;  
    myvector.push_back(mystruxt);  
  
    mystruxt.price = 41.00;  
    myvector.push_back(mystruxt);  
  
    mystruxt.price = 22.50;  
    myvector.push_back(mystruxt);  
  
    mystruxt.price = 11.00;  
    myvector.push_back(mystruxt);  
  
    threshold = 30.34;  
    //threshold = 10.00;  
    std::vector<MyStruct>::iterator it =   
        std::find_if(myvector.begin(), myvector.end(), PriceRanges);  
  
    if (it != myvector.end())  
    {  
        std::cout << std::fixed;  
        std::cout << std::setprecision(2);  
        std::cout << "The first value <= threshold of "  
            << threshold << " is " << it->price << '\n';  
    }  
    else   
    {  
        std::cout << "No struct found in vector with a Price <= "  
            << threshold << std::endl;  
    }  
  
    return 0;  
}  
  
  

Obviously, a lambda could be used instead of a predicate function
for those so-inclined.

• Wayne

Answer 2

but now we have here also an array [=]

There is no "array" involved in that code or any of the
other that has been posted in this thread. The symbols
[] and [=] in the code posted is the first part of a
lambda, known as the "capture clause (Also known as the
lambda-introducer in the C++ specification.)" See
the docs for a description of all of the parts of a
lambda expression:

Lambda expressions in C++
https://learn.microsoft.com/en-us/cpp/cpp/lambda-expressions-in-cpp?view=msvc-170

• Wayne