search a structure element in map - c++

Question

i am new to C++(also english).
i want to search {1,2,3} in the map and if it exists , print TRUE on screen
but i can not
my code comes below
can you help me?
#include <iostream>
#include <map>
#include <iterator>
#define PKT_UNIT_MAX_LEN 10000
using namespace std;
struct PKT_UNIT
{
int len;
unsigned int checksum;
unsigned char data[PKT_UNIT_MAX_LEN];
};
int main()
{
map<int,PKT_UNIT> maharan;
maharan.insert(pair<int,PKT_UNIT>(1,{1,2,3}));
map<int,PKT_UNIT> ::iterator it;
it=maharan.begin();
for(it=maharan.begin(); it != maharan.end(); it++ )
{
if (maharan.find(it)!=maharan.end())
{
if (it->second.len==1 && it->second.checksum==2 && it->second.data==3)
cout<<"TRUE"<<endl;
}
return 0;
}

Answer 1

map::find takes something comparable to the key_type, not the mapped_type, and certainly not an iterator. Searching for the value is not what std::map is designed to support. You can instead use the generic searching algorithms.
bool operator==(const PKT_UNIT& lhs, const PKT_UNIT& rhs)
{
return (lhs.len == rhs.len)
&& (lhs.checksum == rhs.checksum)
&& std::equal(lhs.data, lhs.data + lhs.len, rhs.data);
}
int main()
{
PKT_UNIT needle{1,2,3};
std::map<int,PKT_UNIT> maharan;
maharan.insert(pair<int,PKT_UNIT>(1,needle));
auto it = std::find_if(maharan.begin(), maharan.end(), [&needle](auto & item){ return item.second == needle; });
if (it != maharan.end())
{
std::cout << "TRUE";
}
return 0;
}

Answer 2

You should overload the equality operator for PKT_UNIT. Then you should just use std::map::find to find what you are looking for.
bool operator==(const PKT_UNIT& lhs, const PKT_UNIT& rhs)
{
return (lhs.len == rhs.len) &&
(lhs.checksum == rhs.checksum) &&
std::equal(lhs.data,lhs.data + PKT_UNIT_MAX_LEN,rhs.data);
}
The you can do something like this:
PKT_UNIT goal {1,2,3};
for (const auto& e : maharan)
{
if (e.second == goal)
{
std::cout << "TRUE\n";
break;
}
}
Also, as it seems you don't need the key, maybe you want to use std::set and use a search algorithm, or std::unordered_set, in which case you wouldn't need a search algorithm at all.