String and const char *

I am reading some documents about c++ and it says:In c++ string is equals to const char *.Is this true?
Because i compile this code:

Code:

#include <iostream>
#include <string>
using namespace std;
int main() {
	const char * p="ppppp";
	string s="aaaaaaaa";
	s+="eeeee";
	s=p;
	p=s;//gives error:error C2440: '=' : cannot convert from 'std::string' to 'const char *'	
}

Isn't string equals to const char *?If equals why does this error occur and why does compiler give permission to change value of string s after initializition?

It is probably referring to a string in general, not the C++ string class. In C++, there is a standard class called string that should be used for string processing. That is different than const char* and has different properties. One property is that you can assign a C style string (char* or const char*) to it, and a copy is made and stored in the string. That is why you can change the string.

A string is a sequence of characters.

A C-style string is sequence of characters stored in a char array with the last character being a '\0'.

A C++ string is a special C++ type called 'string' that was created to make handling a sequence of characters much easier than in C.

And a string literal ( "hello" ) ought to be of type const char[<length of string + 1>], which is implicitely convertible to const char*, but is in practice usually char[<length of string + 1>] for backwards compatibility. The standard might even require this.

> p=s;//gives error:error C2440: '='
You could do
p = s.c_str();

This allows you to view the contents of your C++ string as a const char *

Note the const is very important, since if you try and cast that const away as a means of modifying the C++ string through the back door, then you're going to break something.

why does compiler give permission to change value of string s after initializition?

Because the C++ string type is defined to allow you to do that.