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Assuming size of char is one byte this can be implemented as following macro.

#define mysizeof(data) (char *)(&data+1)-(char *)(&data)


U can also make it function , but C doesnt support fn overloading

In case of C++ this can be implemented with a template function, and it can work for object and type as well..

Any Idea how to implement in JAVA

Good solution.. Can you explain how this is working for an array? I thought for int a[]={4,5,6}; would give me 4 instead of 12. but it does correctly give me 12;

suppose memory location for a[] starts with 2000, then a[]+1 will point to 2012 and not 2004.
This is because a[] is referring to the complete array and hence a[]+1 will refer to a memory location just next to the last element of the array.
So, the output with mysizeof(a) gives you 12 and not 4.

one complicate way to implement this is to use RTTI, using typeid and calculate the size of certain data.

why do we have to cast it with (char *) can anybody please explain?

what is the code for getting the size of structure??
for eg:
struct node{
char c;
int i;
};

#define my_sizeof(d) ({ \$
typeof(d) _a; \$
(size_t) ((char *)(&_a + 1)-(char*)(&_a)); })$

This will work for all standard & user data types.

#define my_sizeof(d) ({            \$
          typeof(d) _a;            \$
         (size_t) ((char *)(&_a + 1)-(char*)(&_a)); })$

This will work for all standard & user defined data types

#define my_sizeof(d) ({            \$
          typeof(d) _a;            \$
         (size_t) ((char *)(&_a + 1)-(char*)(&_a)); })$

This will work for all data types

Someone has asked sizeof(type). I have the answer but with a little bit modification to signature. - sizeof(type, size) - here size if the output parameter name. Refer this example-

#include<iostream>
#include<string>

using namespace std;

#define mysize(x,y) { \
x *p; \
y = (char*)(p+1) - (char*)p; \
}


int main()
{
int size = 0;
mysize(int, size);
cout << "size = " << size << endl;
}

A trick to get sizeof(type) but with a modified signature -

#include<iostream>
#include<string>

using namespace std;

#define mysize(x,y) { \
        x *p; \
        y = (char*)(p+1) - (char*)p; \
}


int main()
{
  int size = 0;
  mysize(int, size);
  cout << "size = " << size << endl;
}

Here is an implementation.


#define my_sizeof(type) (char *)(&type+1)-(char*)(&type)
int main()
{
double x;
printf("%d", my_sizeof(x));
getchar();
return 0;
}
You can also implement using function instead of macro, but function implementation cannot be done in C as C doesn’t support function overloading and sizeof() is supposed to receive parameters of all data types.

Note that above implementation assumes that size of character is one byte.

Time Complexity: O(1)
Space Complexity: O(1)

#define MYSIZEOF(X) ((X*)0 +1)
int main()
{
printf ("%d", MYSIZEOF(int));
return 0;
}

Microsoft india has idiots.