how to initialize a char array?

Question

char * msg = new char[65546];

want to initialize to 0 for all of them. what is the best way to do this in C++?

Answer 1

memset(msg, 0, 65546)

Answer 2

This method uses the 'C' memset function, and is very fast (avoids a char-by-char loop).

const uint size = 65546;
char* msg = new char[size];
memset(reinterpret_cast<void*>(msg), 0, size);

Answer 3

memset or calloc.

Answer 4

char * msg = new char[65546]();

It's known as value-initialisation, and was introduced in C++03. If you happen to find yourself trapped in a previous decade, then you'll need to use std::fill() (or memset() if you want to pretend it's C).

Note that this won't work for any value other than zero. I think C++0x will offer a way to do that, but I'm a bit behind the times so I can't comment on that.

UPDATE: it seems my ruminations on the past and future of the language aren't entirely accurate; see the comments for corrections.

Answer 5

The "most C++" way to do this would be to use std::fill.

std::fill(msg, msg + 65546, 0);

Answer 6

what is the best way to do this in C++?

Because you asked it this way:

std::string msg(65546, 0); // all characters will be set to 0

Or:

std::vector<char> msg(65546); // all characters will be initialized to 0

If you are working with C functions which accept char* or const char*, then you can do:

some_c_function(&msg[0]);

You can also use the c_str() method on std::string if it accepts const char* or data().

The benefit of this approach is that you can do everything you want to do with a dynamically allocating char buffer but more safely, flexibly, and sometimes even more efficiently (avoiding the need to recompute string length linearly, e.g.). Best of all, you don't have to free the memory allocated manually, as the destructor will do this for you.

Answer 7

Absent a really good reason to do otherwise, I'd probably use:

std::vector<char> msg(65546, '\0');

Answer 8

You can use a for loop. but don't forget the last char must be a null character !

char * msg = new char[65546];
for(int i=0;i<65545;i++)
{
    msg[i]='0';
}
msg[65545]='\0';