Does a pointer returned by std::string.c_str() or std::string.data() have to be freed?

问题

As far as i know, std::string creates a ident array-copy of its content when you call the c_str()/data() methods (with/out terminating NUL-char, does not matter here). Anyway, does the object also take care of freeing this array or do I have to?

In short:

std::string hello("content");

const char* Ptr = hello.c_str();

// use it....

delete[] Ptr;   //// really ???

I just want to be on the safe side when it comes to memory allocation.

回答1:

No you don't need to deallocate the ptr pointer.

ptr points to a non modifyable string located somewhere to an internal location(actually this is implementation detail of the compilers).

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Reference:

C++ documentation:

const char* c_str ( ) const;

Get C string equivalent

Generates a null-terminated sequence of characters (c-string) with the same content as the string object and returns it as a pointer to an array of characters.

A terminating null character is automatically appended.

The returned array points to an internal location with the required storage space for this sequence of characters plus its terminating null-character, but the values in this array should not be modified in the program and are only guaranteed to remain unchanged until the next call to a non-constant member function of the string object.

回答2:

No need, the dtor of the string class will handle the destruction of the string so when 'hello' goes out of scope it is freed.

回答3:

std::string handles this pointer so don't release it. Moreover, there are two limitations on using this pointer:
1. Don't modify string that is pointed by this pointer, it is read-only.
2. This pointer may become invalid after calling other std::string methods.

回答4:

Not only you don't need to free the pointer but you in fact should not. Otherwise the destructor of std::string will attempt to free it again which may result in various errors depending on the platform.

回答5:

The std::string class is responsible for freeing the memory allocated to contain the characters of the string when an object of the class is destructed. So if you do

delete[] Ptr;

before or after hello object is destructed (leaves the C++ {} scope it was created in), your program will run into a problem of trying to free a memory block that is already freed.

来源：https://stackoverflow.com/questions/7460753/does-a-pointer-returned-by-stdstring-c-str-or-stdstring-data-have-to-be