Why must a pointer to a char array need strcpy to assign characters to its array and double quotes assignment will not work?

Question

The first example does not work when you go to delete the pointer. The program either hangs when I add the null terminator or without it I get:

Debug Assertion Fai

Answer 1

There are 3 things to understand:

1) char *at; is just a pointer variable.
A pointer variable simply means that it holds a memory address.

2) new char[3] returns the starting address of the memory allocated on the heap.

3) "hello" returns the address of the string literal.

char *at = new char [3];
//at now contains the address of the memory allocated on the heap


at = "hello";
//at now contains the address of the static string. 
// (and by the way you just created a 3 byte memory leak)


delete[] at; 
//WOOPS!!!! you can't do that because you aren't deleting 
// the original 3 chars anymore which were allocated on the heap!
//Since at contains the string literal's memory address you're 
// trying to delete the string literal.

A note about modifying read only memory:

Also you should never be modifying a string literal. I.e. this should never be done:

char *at = "hello";
at[2] = '\0'; 

The memory for string literals must be read only and if you change it, the results are undefined by the C++ language.

Since you're using C++:

Since you're using C++ please consider using the std::string type instead.

#include 

using namespace std;

int main(int argc, char **argv)
{
  string s = "hello";
  s += " world!";

  //s now contains "hello world!"

  s = "goodbye!";

  //Everything is still valid, and s contains "goodbye!"


  //No need to cleanup s. 

  return 0;
}