In C, why can't the value of a pointer-to-char variable be changed after it has been assigned?

Question

I don't understand the difference between this case:

#include <stdio.h>

int main()
{
  int i = 0;
  i = 1;

  return 0;
}

And this case:

#include <stdio.h>

int main()
{
  char *mychar = "H";
  *mychar = "E";

  return 0;
}

Which produces the compiler warning "assignment makes integer from pointer without a cast".

Shouldn't *mychar = "E" dereference mychar to assign it the value of "E"?

Many thanks.

Answer 1

You have confused few things.

• Note "E" is actually const char[] which stores 'E' and '\0'. It is not a single character. For single characters you use '', like 'E'.
• mychar points to string literal and you can't change string literals.

If what you had in mind is this:

 char *mychar = "H";
 mychar = "E"; 

This is ok, you are not changing the string literal, just first time the pointer mychar points to string literal "H", then to "E".

This you can't do:

  char *mychar = "Hello";
  *mychar = 'E'; // Can't modify the string literal

But this you can do:

  char c = 0;
  char *mychar = &c;
  *mychar = 'E'; // This is ok