char* and cin in C++

Question

I would like to input a string of indefinite length to a char * variable using cin;

I can do this:

char * tmp = "My string";
cout << tmp << endl;
system("pause");

It works perfectly.

But I fail to do this:

 char * tmp
 cin >> tmp;

Could you give me a hing what's wrong"

Answer 1

Well, you havn't created an object for the char* to point to.

char* tmp = new char[MAX_LENGTH];

should make it work better (you have to define MAX_LENGTH). Another way to do this is:

std::string strtmp;
cin >> strtmp;
const char* tmp = strtmp.c_str();

This method would mean that you need not use new.

Answer 2

Couple of issues:

char * tmp
cin >> tmp;

tmp is not allocated (it is currently random).

operator>> (when used with char* or string) reads a single (white space separated) word.

Issue 1:

If you use char* and allocate a buffer then you may not allocate enough space. The read may read more characters than is available in the buffer. A better idea is to use std::string (from this you can get a C-String).

Issue 2:

There is no way to read indefinite string. But you can read a line at a time using std::getline.

std::string line;
std::getline(std::cin, line);

char* str = line.data();