I use visual studio 2017
int main() { std::string a = "hello"; std::cout << &a; a[1] = 'r'; std::cout << &a; gives same address as above std::cin.get(); } when i hover the mouse pointer over "hello".
It shows const char[6]. So "hello" is stored in read only memory.
then how come it is possible to change the value in it.
where string literals will be stored
String literals have static storage duration.
then how come it is possible to change the value in it.
You didn't change the string literal (which is something that cannot be done in C++).
You've created an object of type std::string. std::string contains a (potentially) dynamically allocated buffer. You've copied the string literal into that dynamic buffer, and you're modifying the copy of the string literal.
But with "hrllo".It should allocate new memory for "hrllo" right? and make a to point to new location?
No. Modifying characters of a std::string will not cause reallocation. Inserting characters however may potentially cause reallocation.
std::string.The std::string makes a copy of "hello" and you didn't make the std::string itself const.
The literal "hello" sits in read-only memory of the executable, which is there even before the program runs. The variable ais constructed from the literal through:
string::string(const char*) (actually std::basic_string)
This constructor copies the characters from the literal to the newly created object. If the string is short, then the characters may be copied directly to the memory of the object. Otherwise, a new memory area is allocated, the characters are copied there, and the object points to the new block.
Never does the new object store a pointer to the original literal.
The lines
std::cout << &a; Takes the address of the object (named a) of type std::basic_string<char>. This object sits on the stack, and is created and destroyed inside int main(). The object does not move, so the pointer is constant and does not change when the string changes. This is the same as the this pointer inside the methods of the std::basic_string<char> of this object.
a internally stores the address of a copy of "hello". It does not just point to a constant.
a copies the characters pointed by a. It may store it in-place (short string optimization) or allocate a new memory block, copy the string there, and put the new pointer into a
aisn't a string literal. It's astd::stringthat was constructed using a string literal, but it has its own copy of the data, possibly on the heap. Try"hello"[1] = 'r';and you'll almost certainly get a crash."hello"? I can only see you changinga.42is an integer constant.int a = 42; std::cin >> a;modifies the variablea; that does not mean it is possible to change the value of integer constants.std::string_view(to avoid the copy that std::string does)