I have a map of maps as follows:
std::map<char,std::map<short,char>> my_maps;
and I need to return a refrence to one of the maps corresponding to an specified key from a function.
I do not know how I should do this ,here is my code:
bool GetMap(char key,std::unique_ptr<std::map<short,char>> my_map){
auto m=my_maps.find(key);
if(m!=my_maps.end()){
my_map=m->second;
// I have also tried this: my_map=my_maps[_commandcode];
return(true);
}
return (false);
}
This is what I will do instead:
std::map<short,char>& GetMap(char key, std::map<char,std::map<short,char>> &my_maps)
{
auto m = my_maps.find(key);
if (m != my_maps.end())
{
return m->second;
}
throw std::exception("not found");
}
Related
I'm working on a game and I'm trying to add collectables. I'm trying to remove the object from the list after the player has collided with it, but it ends up crashing and says:
Unhandled exception thrown: read access violation.
__that was 0xDDDDDDE9.
It says this on the for loop statement, but I think it has to do with the remove_if() function.
Here is my code:
for (sf::RectangleShape rect : world1.level1.brainFrag) {
collides = milo.sprite.getGlobalBounds().intersects(rect.getGlobalBounds());
if (collides == true) {
world1.level1.brainFrag.remove_if([rect](const sf::RectangleShape val) {
if (rect.getPosition() == val.getPosition()) {
return true;
}
else {
return false ;
}
});
brainFrag -= 1;
collides = false;
}
}
if (brainFrag == 0) {
milo.x = oldPos.x;
milo.y = oldPos.y;
brainFrag = -1;
}
I don't understand your approach, you loop the rects, then when you find the one you want to remove, you search for it again through list<T>::remove_if.
I think that you forgot about the fact that you can use iterators in addition to a range-based loop:
for (auto it = brainFrag.begin(); it != brainFrag.end(); /* do nothing */)
{
bool collides = ...;
if (collides)
it = world1.level1.brainFrag.erase(it);
else
++it;
}
This allows you to remove the elements while iterating the collection because erase will take care of returning a valid iterator to the element next to the one you removed.
Or even better you could move everything up directly:
brainFrag.remove_if([&milo] (const auto& rect) {
return milo.sprite.getGlobalBounds().intersects(rect.getGlobalBounds())
}
A side note: there's no need to use an if statement to return a boolean condition, so you don't need
if (a.getPosition() == b.getPosition()
return true;
else
return false;
You can simply
return a.getPosition() == b.getPosition();
I have a program to verify if an IPv4 address entered as string is in valid dotted-quad notation.
The problem I am facing is that I'm not able to return (exit) function once I detect error. As per cppreference documentation for_each returns UnaryFunction. I tried using any_of and all_of but they require me using an loop (range-based loop) inside my lambda function which I'm trying to avoid. Am I missing something or it is not possible to return value in for_each.
vector<string> ipExplode;
string ip;
bool inValidIp = false;
cout << "Server IP : ";
cin >> ip;
trim(ip);
ipExplode = explode(ip, '.');
if(not for_each(ipExplode.begin(), ipExplode.end(), [](const string& str) -> bool{
int32_t ipNum;
if(regex_search(str, regex("\\D+")))
return false;
try
{
ipNum = stoi(str);
if(ipNum < 0 or ipNum > 255)
return false;
}
catch (std::exception& ex)
{
return false;
}
}))
return false;
from for_each:
If f returns a result, the result is ignored.
i.e. there is no point in returning a value from your for_each lambda.
A good choice here is all_of, which accepts a UnaryPredicate rather than a UnaryFunction, since you want to make sure that all of the parts of the string pass the lambda successfully:
bool isValid = std::all_of(ipExplode.begin(), ipExplode.end(), [](const std::string& str) -> bool{
if(regex_search(str, regex("\\D+")))
return false;
try
{
int32_t ipNum = stoi(str);
if(ipNum < 0 or ipNum > 255)
return false;
}
catch (std::exception& ex)
{
return false;
}
return true;
});
all_of will stop iterating once an invalid part is found.
Am I missing something or it is not possible to return value in for_each.
for_each does return the UnaryFunction. But if you put a unary function to if expression, its meaningless.
In your case, a lambda without capturing can implicitly convert to a function pointer. A non-null function pointer as a boolean value is always true. Thus your
if(not for_each( /* ... */ ))
will be evaluated to false all the time.
As commentators and other answerers have already written, std::all_of is what you want here.
You shouldn't use for_each anyway. Replace it by the ranged-based for and it all becomes so much simpler and elegant. Put it all in a function and there you go:
auto is_ip_valid(const std::vector<std::string>& ipExplode)
{
for (auto&& str : ipExplode)
{
// ...
}
}
Using C++11, I'd like to iterate over a vector and return a type that indicates that the index was not found.
I am use to the traditional for(;;) loop and specifying the index manually, as my code shows below.
inline std::size_t ItemList::FindItem(Items& Item)
{
for (std::size_t i = 0; i < ItemVector.size(); i++)
{
if (ItemVector[i]->GetId() == Item.GetId() && !ItemVector[i]->GetName().compare(Item.GetName()))
{
return i + 1;
}
}
return 0;
}
I'm also having to increment the index +1 in order to return a value of 0 (to accommodate unsigned size_t) to indicate the calling method that the index was not found (I understand this is asinine). I am assuming it would be more suitable to return something more like std::end()?
Would using a C++11 iterator approach be more efficient? The vector will populate to a large number and the find needs to be quick.
You could use std::find_if and work with iterators:
auto it = std::find_if(ItemVector.begin(), ItemVector.end(),
[&Item](Items *value) {
return value->GetId() == Item.GetId() && !value->GetName().compare(Item.GetName());
}
);
Then you can simply test if it != ItemVector.end() to know if you found something.
There will likely be no (or very small) difference between this and your version in term of speed, but it is a cleaner way to check if something was found or not.
Yes, an iterator would be the way to do this, you're actually writing your own version of find_if You could instead do:
find_if(cbegin(ItemVector), cend(ItemVector), [&](const auto& i){ return i.GetId() == Item.GetId() && i.GetName() != Item.GetName(); })
You can test whether the result of this function was found by testing for equality with cend(ItemVector).
Additionally if you need to find the index of the item you can pass this result after cbegin(ItemVector) to: distance
Live Example
My solution for double search condition that Lambda has multiple parameters in find_if
bool check_second_loop(FullFrame *image_track, guint64 object_id, bool *deletion)
{
auto itr= std::find_if(image_track->track_ids.begin(),
image_track->track_ids.end(),
[object_id](const guint64& a)
{
return a == object_id;
});
if (itr != image_track->track_ids.end())
{
image_track->track_ids.erase(itr);
if(image_track->track_ids.size()==0)
{
*deletion = true;
}
return true;
}
else
return false;
}
bool check_first_loop(guint64 object_id, gint source_id)
{
bool deletion = false;
auto it = find_if(full_frame_list.begin(), full_frame_list.end(),
[object_id, &deletion, source_id](FullFrame &x)
{
return check_second_loop(&x, object_id, &deletion)
&& x.camera_number == source_id;
});
if (it != full_frame_list.end())
{
// Found
return true;
}
else
return false;
}
I'm having some trouble with the following method and I need some help trying to figure out what I am doing wrong.
I want to return a reference to a Value in a document. I am passing the Document from outside the function so that when I read a json file into it I don't "lose it".
const rapidjson::Value& CTestManager::GetOperations(rapidjson::Document& document)
{
const Value Null(kObjectType);
if (m_Tests.empty())
return Null;
if (m_current > m_Tests.size() - 1)
return Null;
Test& the_test = m_Tests[m_current];
CMyFile fp(the_test.file.c_str()); // non-Windows use "r"
if (!fp.is_open())
return Null;
u32 operations_count = 0;
CFileBuffer json(fp);
FileReadStream is(fp.native_handle(), json, json.size());
if (document.ParseInsitu<kParseCommentsFlag>(json).HasParseError())
{
(...)
}
else
{
if (!document.IsObject())
{
(...)
}
else
{
auto tests = document.FindMember("td_tests");
if (tests != document.MemberEnd())
{
for (SizeType i = 0; i < tests->value.Size(); i++)
{
const Value& test = tests->value[i];
if (test["id"].GetInt() == the_test.id)
{
auto it = test.FindMember("operations");
if (it != test.MemberEnd())
{
//return it->value; is this legitimate?
return test["operations"];
}
return Null;
}
}
}
}
}
return Null;
}
Which I am calling like this:
Document document;
auto operations = TestManager().GetOperations(document);
When I inspect the value of test["operations"] inside the function I can see everything I would expect (debug code removed from the abode code).
When I inspect the returned value outside the function I can see that it's an array (which I expect). the member count int the array is correct as well, but when print it out, I only see garbage instead.
When I "print" the Value to a string inside the methods, I get what I expect (i.e. a well formated json), but when I do it outside all keys show up as "IIIIIIII" and values that aren't strings show up correctly.
rapidjson::StringBuffer strbuf2;
rapidjson::PrettyWriter<rapidjson::StringBuffer> writer2(strbuf2);
ops->Accept(writer2);
As this didn't work I decided to change the method to receive a Value as a parameter and do a deep copy into it like this
u32 CTestManager::GetOperationsEx(rapidjson::Document& document, rapidjson::Value& operations)
{
(...)
if (document.ParseInsitu<kParseCommentsFlag>(json).HasParseError())
{
(...)
}
else
{
if (!document.IsObject())
{
(...)
}
else
{
auto tests = document.FindMember("tests");
if (tests != document.MemberEnd())
{
for (SizeType i = 0; i < tests->value.Size(); i++)
{
const Value& test = tests->value[i];
if (test["id"].GetInt() == the_test.id)
{
const Value& opv = test["operations"];
Document::AllocatorType& allocator = document.GetAllocator();
operations.CopyFrom(opv, allocator); //would Swap work?
return operations.Size();
}
}
}
}
}
return 0;
}
Which I'm calling like this:
Document document;
Value operations(kObjectType);
u32 count = TestManager().GetOperationsEx(document, operations);
But... I get same thing!!!!
I know that it's going to be something silly but I can't put my hands on it!
Any ideas?
The problem in this case lies with the use of ParseInSitu. When any of the GetOperations exist the CFileBuffer loses scope and is cleaned up. Because the json is being parsed in-situ when the buffer to the file goes, so goes the data.
For example I have an vector of objects and they all have attribute PointX so I want to check if all of them have the same value of PointX and if they have it should return true or false whatever.
So in a kind of pseudo-code:
IF ( Object[1].getPointX() == Object[2].getPoint(x) == Object[3].getPoint(x) ){
return true;
}
The problem is that I have more than 55 objects so there has to be a way to compare them without writting them all individually. I know there must be with a for loop but still I have no idea.
thanks in advance.
edit:
#awesomeyi your suggestion seems the easiest and more adequate to my needs (I'm not saying the others are not but I think they are too complicated for a newb like me) but it's not working, even if Xpoints are all the same or different it always returns false. here's what i have:
bool allKilled(){
auto checkpointx = Invader[0].getIfActive();
for(int i = 0; i < 55; ++i){
if(Invader[i].getIfActive() != checkpointx){
return false;}
}
}
the getIfActive() just returns if its true or false, and i want this method to return true if all Active (attribute of the object) of all objects are all false.
Something like this:
auto refx = Object[0].getPointX();
bool b = std::all_of(Object.begin(),
Object.end(),
[refx](TheTypeOfTHeElements& e)
{ return e.getPointX() == ref; });
Obviously you need to check that Objects is not empty.
For loop?
auto checkpointx = Object[0].getPointX();
for(int i = 1; i < Object.size(); ++i){
if(Object[i].getPointX() != checkpointx)
return false;
}
I'd do it something like this:
template<typename Objects, typename Comparison>
bool is_all_same( Objects&& objects, Comparison&& comp ) {
using std::begin; using std::end;
auto&& b = begin(objects);
auto&& e = end(objects);
if (b == e)
return true;
auto&& first = *b;
for( auto&& cur = std::next(first); cur != e; ++cur ) {
if (!comp( first, cur ))
return false;
}
return true;
}
use:
bool all_same_x = is_all_same( objs, []( Obj const& left, Obj const& right )->bool {
return left.getPointX() == right.getPointX();
});
where objs is some container or range containing objects of type Obj.
The above code should work on all standard containers, C style arrays, custom containers that support the new for loops, and is close to optimal performance wise.