std :: string.assign（const char *）或op =（带有const char *）会创建char *的副本吗？

Question

Digging through the c++ code, it looks like it does a copy, but I cannot be sure. By "copy", I mean something like strcpy is happening internally. And std:string doesn't end up with a pointer to the same char* internally it was passed.

const char *somestring = ...
std::string str;
str.assign(somestring);
// or
str = somestring;  //in my impl, op= calls to assign(const char*)

Answer 1

std::string will always copy from the array pointed to by a char * . You can also provide an iterator range in some constructors.

Copy or reference counting during copies of one std::string to another depends on the C++ library that you are using.

The C++ 2011 standard requires std::string to make real copies. The 2003 standard allowed reference counted copies.

The GNU libstdc++ uses reference counted strings. And for backward compatibility, even the 2011 standard GCC builds with them. Otherwise it couldn't link to code built with the 2003 standard.

There is a preprocessor definition to turn on the new behavior.

See also std::string copy constructor NOT deep in GCC 4.1.2? and Is std::string refcounted in GCC 4.x / C++11?