3 ms·

In C++, can't you just get a reference to the first character in the std::string and use it like a C-style string ?

jcranmer 8y ago
std::string isn't null-terminated. You need to use .c_str(), which allocates a copy that is destroyed when the string is changed (or is destructed).
- TimJYoung 8y ago
  Ahh, yes, forgot about that - thanks !
- thestoicattack 8y ago
  It seems[1] that since C++11 .data() and .c_str() are the same function. c_str() is also documented as having constant complexity. If it made a copy, wouldn't it have to be linear? [1] https://en.cppreference.com/w/cpp/string/basic_string/data https://en.cppreference.com/w/cpp/string/basic_string/data
  - gpderetta 8y ago
    Yes. Allocating on demand was a legal implementation before c++11. No standard library made use of the option and the latitude was removed in c++11. I think it is still allowed to null terminate on demand.
  - hermitdev 8y ago
    It doesn't have to make a copy. std::string is always null-terminated as of C++11.
- vortico 8y ago
  In practice, all modern C++ compilers and standard libraries just set a null character to the c_str()[len] position and reallocate the string if the capacity of the string buffer cannot contain the extra byte. It is never a linear operation unless you're working with old or niche C++ compilers. In C++11 this is required in the standard.
vortico 8y ago
Yes, it is easy to go back and forth between std::string and char* using the std::string constructor and ::c_str(). The "nightmare" part is that when interacting with C from C++, you can never work with the internal std::string data, so you have to manage copies of buffers and copy it back into a std::string every single time you interact with C functions. It's really nasty to look at in large quantities.
- TimJYoung 8y ago
  Ahhh, okay, now I see the objection. Object Pascal allows you to use them interchangeably as you see fit with simple typecasts.

std::string isn't null-terminated. You need to use .c_str(), which allocates a copy that is destroyed when the string is changed (or is destructed).

TimJYoung 8y ago
Ahh, yes, forgot about that - thanks !
thestoicattack 8y ago
It seems[1] that since C++11 .data() and .c_str() are the same function. c_str() is also documented as having constant complexity. If it made a copy, wouldn't it have to be linear? [1] https://en.cppreference.com/w/cpp/string/basic_string/data https://en.cppreference.com/w/cpp/string/basic_string/data
- gpderetta 8y ago
  Yes. Allocating on demand was a legal implementation before c++11. No standard library made use of the option and the latitude was removed in c++11. I think it is still allowed to null terminate on demand.
- hermitdev 8y ago
  It doesn't have to make a copy. std::string is always null-terminated as of C++11.
vortico 8y ago
In practice, all modern C++ compilers and standard libraries just set a null character to the c_str()[len] position and reallocate the string if the capacity of the string buffer cannot contain the extra byte. It is never a linear operation unless you're working with old or niche C++ compilers. In C++11 this is required in the standard.

vortico 8y ago

Yes, it is easy to go back and forth between std::string and char* using the std::string constructor and ::c_str(). The "nightmare" part is that when interacting with C from C++, you can never work with the internal std::string data, so you have to manage copies of buffers and copy it back into a std::string every single time you interact with C functions. It's really nasty to look at in large quantities.

TimJYoung 8y ago
Ahhh, okay, now I see the objection. Object Pascal allows you to use them interchangeably as you see fit with simple typecasts.