What is ** in C++?

Question

I\'ve seen some code, as well as some errors generated from my compiler that have a \'**\' token before the variable (eg **variablename unreferenced-- or someth

Answer 1

It's a double dereference.

int i = 3;
int* ptr_to_i = &i;
int** ptr_to_ptr_to_i = &ptr_to_i;

std::cout << **ptr_to_ptr_to_i << std::endl;

Prints 3.

Answer 2

You may recognize the signature for main():

int main(int argc, char* argv[])

The following is equivalent:

int main(int argc, char** argv)

In this case, argv is a pointer to an array of char*.

In C, the index operator [] is just another way of performing pointer arithmetic. For example,

foo[i]

produces the same code as

*(foo + i)

Answer 3

• int **var declares a pointer to a pointer
• **var references the content of a pointer, which in itself points to a pointer

Answer 4

It's not a ** token. It's simply a * token followed by another * token. In your case, you have a pointer to a pointer, and it's being dereferenced twice to get whatever's really being pointed to.

Answer 5

See http://www.c2.com/cgi/wiki?ThreeStarProgrammer