Re: unique value for map
Ashish wrote:
I just gave an example by that structure. My concern was not with char* or
allocating memory, my concern was for using std::map. ok let me write it
typedef struct tree
'typedef struct' is C-style, and is never necessary in C++. Just do:
struct MyTree
{
int id;
std::string name;
std::map<> mapobject; // object not pointer
struct tree *left;
MyTree *left;
is fine with the above change.
struct tree * right;
struct tree * child;
struct tree * parent;
}MyTree;
Generally, in idiomatic C++ coding you rarely use the 'struct' keyword,
and rarely have any public member variables, and instead use classes
with member functions. You would have a constructor to create the
object. This makes it easier to separate the code implementing the tree
from the code using it, and will make it easier to change your structure.
MyTree * treeobject = (MyTree*)malloc(sizeof(struct tree));
or i can use
MyTree * treeobject = new MyTree;
You must use the latter - the former will not initialize mapobject
correctly.
the total memory for treeobject (as per my knowledge) in win32 application
4(id) + 16(size of std::string class) + 16(size of std::map class) + 4(left)
+ 4(right) + 4(child) + 4(parent)
+ possibly some fixed padding. But this is just the direct memory - the
string object and map object will allocate additional memory from the
heap to store their data.
Now to insert any data in map
treeobject ->mapobject.insert(...).
I did not use map before, i thought without using map pointer we can not use
map in a tree(above structure) where we allocate memory, thats why i put a
query in this thread. I was not aware that when we insert data in mapi it's
std::map class headeche which allocate run time memory and it allocate b'se
mapobject contains an address not a value.
This is how all properly written objects work - they manage their own
memory without you having to worry about it. However, you have to make
sure that you use 'new' to allocate the object containing the map, so
that it is correctly initialized, and 'delete' to destroy that object,
otherwise you will get a memory leak. However, you can avoid using
'delete' directly if you use a smart pointer class.
And why i cant use chatacter pointer (char* name) in above structure. I can
allocate memory to it as i want. If i have a very big string(around 1000
character) then will std::string works successfully.
Of course - std::string just simplifies your code by managing the memory
automatically. I'd recommend reading a modern C++ book, such as
Accelerated C++ http://www.acceleratedcpp.com/. You might be able to
find some decent online tutorials for the C++ Standard Library
(sometimes erroneously called the STL).
Tom