What is copy on write string?

COW, short for copy on write, is a way to implement mutable strings so that creating strings and logically copying strings, is reduced to almost nothing; conceptually they become free operations like no-ops. In particular, would the same reason or reasons apply to a reference counted immutable string value class?

What is __ cxx11?

If you get linker errors about undefined references to symbols that involve types in the std::__cxx11 namespace or the tag [abi:cxx11] then it probably indicates that you are trying to link together object files that were compiled with different values for the _GLIBCXX_USE_CXX11_ABI macro.

What is the size of std::string?

24 bytes
While std::string has the size of 24 bytes, it allows strings up to 22 bytes(!!) with no allocation.

Why is copy-on-write needed?

Copy-on-write finds its main use in sharing the virtual memory of operating system processes, in the implementation of the fork system call. Typically, the process does not modify any memory and immediately executes a new process, replacing the address space entirely.

What is copy-on-write in fork?

Copy on Write or simply COW is a resource management technique. One of its main use is in the implementation of the fork system call in which it shares the virtual memory(pages) of the OS. In UNIX like OS, fork() system call creates a duplicate process of the parent process which is called as the child process.

When did C++ get strings?

1998
The std::string type is the main string datatype in standard C++ since 1998, but it was not always part of C++. From C, C++ inherited the convention of using null-terminated strings that are handled by a pointer to their first element, and a library of functions that manipulate such strings.

Does C++ have a string type?

Recall that C++ supports two types of strings: The C-style string (or C-String) in header cstring (ported over from C’s string. h ), which represents a string as a char array terminated by a null character ‘\0’ (or 0) (null-terminated char array). The new C++ string class in header string .

What is undefined reference?

An “Undefined Reference” error occurs when we have a reference to object name (class, function, variable, etc.) Thus when the linker cannot find the definition of a linked object, it issues an “undefined reference” error.

How do you find string size?

Using string::size: The method string::size returns the length of the string, in terms of bytes. Using string::length: The method string::length returns the length of the string, in terms of bytes. Both string::size and string::length are synonyms and return the exact same value.

Why is size 32 string?

In other implementations it is not wet (like Jupiter where it is a gas). So this string implementation is 32 because that’s the way it was built in this implementation and it will by 16 in other implementations and 64 in yet another. The size of the string will (like water) depend on the environment it is used in.

Is copy-on-write a viable way to implement a conforming std::string in C++11?

Bookmark this question. Show activity on this post. It had been my understanding that copy-on-write is not a viable way to implement a conforming std::string in C++11, but when it came up in discussion recently I found myself unable to directly support that statement. Am I correct that C++11 does not admit COW based implementations of std::string?

Is GCC’s cow string a valid C++03 implementation?

So GCC’s COW string was a valid C++03 implementation. The C++11 standard no longer permits that behaviour, because no call to operator [] () may invalidate pointers, references or iterators, irrespective of whether they follow a call to data ().

Can I use character types other than char in GCC?

If you want to use character types other than char and wchar_t, such as unsigned char and int, you will need suitable specializations for them. For a time, in earlier versions of GCC, there was a mostly-correct implementation that let programmers be lazy but it broke under many situations, so it was removed.

How to reduce the capacity of a string in GCC?

From GCC 3.4 calling s.reserve (res) on a string s with res < s.capacity () will reduce the string’s capacity to std::max (s.size (), res) . This behaviour is suggested, but not required by the standard.