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

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 2

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

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

Answer 3

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

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

Answer 4

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 5

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 6

memset(msg, 0, 65546)

Answer 7

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';

Answer 8

The C-like method may not be as attractive as the other solutions to this question, but added here for completeness:

You can initialise with NULLs like this:

char msg[65536] = {0};

Or to use zeros consider the following:

char msg[65536] = {'0' another 65535 of these separated by comma};

But do not try it as not possible, so use memset!

In the second case, add the following after the memset if you want to use msg as a string.

msg[65536 - 1] =  '\0'

Answers to this question also provide further insight.

Answer 9

If you panic and can not assign dynamic data to a const char* in a constructor you can insert each element of a dynamic buffer piece by piece. You can even snprintf() to the buffer before making the imprint.

    client_id = new char[26] {
        buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7],buf[8],buf[9],
        buf[10],buf[11],buf[12],buf[13],buf[14],buf[15],buf[16],buf[17],buf[18],buf[19],
        buf[20],buf[21],buf[22],buf[23],buf[24],'\0'
    };

To cover up what you have been doing, maybe the editor has an option where you can set the forecolor same as the background?

Before being fired you can actually prime the const char in the header file declaration with enough space and then later assign real data in the constructor. Great!

const char*  client_id = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";

It is a const pointer and does not have to be initialized before the constructor deals with it.

const char*  client_id;

Answer 10

NOTE: You can write at the top of the page: using namespace std, and thus avoid writing std:: at the beginning of each command.

char * msg = new char[65546]={0}; This command reset all the array to 0.