I am trying to solve an issue using Boost multi_index.
If I have 2 structures as follows:
struct MyStruct1
{
int x;
int y;
};
struct MyStruct2
{
int a;
MyStruct1 b;
};
How would I define an index using MyStruct2::b.x?
Is this possible?
was trying something like:
struct xIndex{};
typedef multi_index_container<
MyStruct2,
indexed_by<
ordered_unique<
tag<xIndex>,
member<MyStruct2, int, &MyStruct2::a::x>
>
>
> MyContainer;
But that doesn't work.
Thanks for any info/advice.
There are several ways to accomplish this but all of them require that you write some boilerplate code. The easiest one is providing a user-defined key extractor:
struct MyStruct2XExtractor
{
typedef int result_type;
int operator()(const MyStruct2& m)const
{
return m.b.x;
}
};
...
typedef multi_index_container<
MyStruct2,
indexed_by<
ordered_unique<
tag<xIndex>,
MyStruct2XExtractor
>
>
> MyContainer;
Related
I have a function called TestFunction which I've simplified down for this question... but in essence, I'm getting an error which says, <function-style-cast> cannot convert from 'initializer list' to std::pair<int, int>. Here's my simplified function:
#include <iostream>
#include <map>
void MyClass::TestFunction(cli::array<int>^ ids){
std::multimap<int, int> mymap;
int count = ids->Length;
for (int i = 0; i < count; ++i) {
//fill in the multimap with the appropriate data key/values
mymap.insert(std::make_pair((int)ids[i], (int)i));
}
}
As you can see, it's a really basic function (when simplified), but I get an error when I try to insert the data into the multimap. Does anyone know why?
I'd either use
mymap.insert(std::make_pair((int)ids[i], (int)i));
or
mymap.emplace((int)ids[i], (int)i);
I'm building off of the answer by #CoryKramer. It appears that if I create a temporary variable of type int and then pass that into the multimap.insert() function... that the error is fixed. Here's the new function:
#include <iostream>
#include <map>
void MyClass::TestFunction(cli::array<int>^ ids){
std::multimap<int, int> mymap;
int count = ids->Length;
for (int i = 0; i < count; ++i) {
//fill in the multimap with the appropriate data key/values
int ff = (int)ids[i];
mymap.insert(std::make_pair(ff, (int)i));
}
}
Out of curiousity... does anyone know why this worked?
In every example I saw that tries to use a dynamic size for an array in a struct uses global constants at some point. What I am trying to do is pass an integer variable that is decided by the user to a structure that I create storing an array of that size, thus dynamic. Obviously the code below doesn't work, but it gives you an idea of what I plan on accomplishing
struct Node {
char input;
int playingBoard[size];
Node* pNext;
};
int main(){
cout<<"enter board size"<<endl;
cin>>size;
int playingBoard[size];
}
struct Node
{
int countr;
int playingBoard[];
};
int countr;
...
struct Node *p = malloc(offsetof(Node, playingBoard) +
countr* sizeof *p->playingBoard);
p->countr= countr;
...
or an independent dynamically-allocated array
struct Node
{
int countr;
int *playingBoard;
};
Node holder;
...
holder.playingBoard =
malloc(holder.countr * sizeof *holder.playingBoard);
i have create one class and i need to use it with vector.
ref class Mur
{
public:
int debutX, debutY;
int finX, finY;
Mur (){}
Mur(int debutX, int debutY) {
this->debutX = debutX;
this->debutY = debutY;
finX = 0;
finY = 0;
}
~Mur()
{
}
int getX() { return debutX; }
int getY() { return debutY; }
bool estFinit() {
return (finX==0);
}
void finir(int x, int y){
finX = x;
finY = y;
}
};
}
When i try to use it
std::vector<Mur^> vMurs;
...
vMurs.push_back(gcnew Mur(i,j));
Error come in file "xmemory" at line 52 but i don't know this file xD
The compiler is objecting because you're trying to store a managed object in an unmanaged class. That cannot work, the garbage collector needs to be able to find object references so it can properly collect garbage. And since it cannot find unmanaged objects, it cannot find the managed reference either.
I'd strongly advice to not use STL/CLR, it combines all the disadvantages of STL with those of the CLR. If you really, really want to use vector<> then gcroot<> can solve the problem. However, using System::Collections::Generic::List<> is by far the best solution.
using namespace System::Collections::Generic;
...
List<Mur^>^ vMurs = gcnew List<Mur^>;
...
vMurs->Add(gcnew Mur(i, j));
I agree with Alexandre C. If you want to use a vector, you could use the STL/CLR (http://msdn.microsoft.com/en-us/library/bb385954.aspx) vector.
Try using
std::vector<gcroot<Mur ^> > vMurs;
...
vMurs.push_back(gcnew Mur(i,j));
I'm new to Objective-C so I'm using a book to get to grips with it. I'm at a bit where it's explaining structs and I can't for the life of me get them to work.
I have the following code:
int main (int argc, char *argv[])
{
struct node
{
int nodeID;
int x;
int y;
BOOL isActive;
};
typedef struct node myNode;
myNode.nodeID = 1;
}
and I'm getting the error written in the title. Every time I search for this error online I found different variations such as 'before '>' token' or 'before '}' token' but i can't find anything with the '.' token and it's really frustrating and I assume it's somethings ridiculously trivial and basic. Any help would be appreciated.
I believe you're trying to modify the actual type itself. nodeA is now the type of that struct, much like int. You need to do something like nodeA myNode, then you would be able to perform myNode.nodeID = 1 without error.
I've got it sorted now, I used the following and it seems to be fixed now:
int main (int argc, char *argv[])
{
struct node
{
int nodeID;
int x;
int y;
BOOL isActive;
};
struct node myNode;
myNode.nodeID = 1;
myNode.x = 100;
myNode.y = 200;
myNode.isActive = TRUE;
}
Thanks for all your help Darth! :)
I think the problem with the original code was, it was trying to make myNode a type name using typedef. Thus, myNode is NOT a variable that assignment can happen to. Rather, it was another alias for struct node.
how to pass multiple arguments in a single function in Objective-C? I want to pass 2 integer values and the return value is also integer. I want to use the new Objective-C syntax, not the old C/C++ syntax.
In objective-c it is really super easy. Here is the way you would do it in C:
int functName(int arg1, int arg2)
{
// Do something crazy!
return someInt;
}
This still works in objective-c because of it's compatibility with C, but the objective-c way to do it is:
// Somewhere in your method declarations:
- (int)methodName:(int)arg1 withArg2:(int)arg2
{
// Do something crazy!
return someInt;
}
// To pass those arguments to the method in your program somewhere:
[objectWithOurMethod methodName:int1 withArg2:int2];
Best of luck!
Since this is still google-able and there are better solutions than the accepted answer; there's no need for the hideous withArg2 – just use colons:
Declaration:
#interface
-(void) setValues: (int)v1 : (int)v2;
Definition:
#implementation
-(void) setValues: (int)v1 : (int)v2 {
//do something with v1 and v2
}
Like this:
int sum(int a, int b) {
return a + b;
}
Called like this:
int result;
result = sum(3, 5);
// result is now 8
More here
int add (int a, int b)
{
int c;
c = a + b;
return c;
}
link text