CODEWITHSUNDEEP
c++
dmeister
dmeister

Reputation: 35654

std::string as C++ byte array

Google's Protocol buffer uses the C++ standard string class std::string as variable size byte array (see here) similar to Python where the string class is also used as byte array (at least until Python 3.0).

This approach seems to be good:

But I am curious: Is that the preferred way for a byte arrays in C++? What are the drawbacks of this approach (more than a few static_casts)

Upvotes: 18

Views: 17076

Answers (3)

Kornel Kisielewicz
Kornel Kisielewicz

Reputation: 57615

std::strings may have a reference counted implementation which may or may not be a advantage/disadvantage to what you're writing -- always be careful about that. std::string may not be thread safe. The potential advantage of std::string is easy concatenation, however, this can also be easily achieved using STL.

Also, all those problems in relation to protocols dissapear when using boost::asio and it's buffer objects.

As for drawbacks of std::vector:

  1. fast assign can be done by a trick with std::swap
  2. data can be accessed via &arr[0] -- vectors are guaranteed (?) to be continious (at least all implementations implement them so)

Personally I use std::vector for variable sized arrays, and boost::array for static sized ones.

Upvotes: 3

avakar
avakar

Reputation: 32685

Personally, I prefer std::vector, since std::string is not guaranteed to be stored contiguously and std::string::data() need not be O(1). std::vector will have data member function in C++0x.

Upvotes: 8

Khaled Alshaya
Khaled Alshaya

Reputation: 96889

I "think" that using std::vector is a better approach, because it was intended to be used as an array. It is true that all implementations(I know and heard of) store string "elements" in contiguous memory, but that doesn't make it standard. i.e. the code that uses std::string like a byte array, it assumes that the elements are contiguous where they don't have to be according to the standards.

Upvotes: 2

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