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Wednesday, November 25, 2009

Multiple Template definion with C++

file.h
template

void tfunc( T a)
{
.........
}

file1.cpp
#include"file.h"
void myfunc1()
{
tfunc(123);
}
file2.cpp
#include"file.h"
void myfunc2()
{
tfunc(456);
}

main.cpp
extern void myfunc1();
extern void myfunc2();

int main()
{
myfunc1();
myfunc2();
return 0;
}


Compile with:
g++ -o main.exe file1.cpp file2.cpp main.cpp


Before you compile, just try answering below questions:
1. Will this compile?
If Yes then Why and how?

If no then you are on right track. Same thing happens with normal function definition. But hold on, c++ template handles this multiple definition problem very smoothly. It means above files will compile and execute properly.
Thats special handling with multiple template instantiation done by linker.

Now you know that this answer of above questions is yes, so you may want to know how and why?
Will post in next post. This question was asked to my friend in NetApp.

Thursday, November 12, 2009

DEShaw Interview Questions

ther are N numbers frm 1 to N and starting from index 1 we will keep deleting every alternate going in cyclic order with array. Only one element will be left at the end.
Tell us the index of element in array we started.

e.g.
there are 5 nums
1 2 3 4 5
then after 1st iteration 1 3 5 will be remained.
.. then 1 will be next to be elliminated and then 5
3 will remain alone...

give sum efficient algorithm to calculate which numer will remain at the end

Answer: 2*(n-2^p)+1
where p=floor(log2 n)

Wednesday, November 11, 2009