Benefits of vector over string?

Question

This question is related to, but not quite the same as, this question.

Are there any benefits to using std::vector instead of std::str

Answer 1

As other answers mention, a vector could be marginally faster since it guarantees contiguous memory, even for small sizes, and doesn't add an extra null byte at the end. However, it is a lot simpler (code-wise) to concatenate two strings than it is to concatenate two vectors:

Using vector:

vector<char> a, b;
// ...
vector<char> c;
c.insert(c.end(), a.begin(), a.end());
c.insert(c.end(), b.begin(), b.end());

Using string:

string a, b;
// ...
string c = a + b;

Answer 2

I think the only benefit you would gain from doing that would the ease of incrementing over the std::vector of characters, but even that can be done with an std::string.

You have to remember that even though std::string seems like an object, it can be accessed like an array, so even accessing specific parts of a string can be done without the use of a std::vector

Answer 3

Ideally one would use vector<unsigned char> to store arbitrary binary data - but I think you already knew this - as you referred to the old question.

Other than that, using vector would definitely be more memory efficient, as string would add a terminating Nul character. Performance might also improve as the allocation mechanism is different for both - vectors guarantee contiguous memory!

Besides that, using a string would not be correct, as callers/users might inadvertently invoking some of the string methods, which could be a disaster.

Answer 4

Yes, vector<char> indeed does have more capabilities over string.

Unlike string, vector<char> is guaranteed to preserve iterators, references, etc. during a swap operation. See: May std::vector make use of small buffer optimization?

Answer 5

std::string on mingw uses 6 pointers and equal 24 bytes. std::vector is always 3 pointers = 12 bytes.

But the fact that std::string uses more tools, makes me question if allocation, appending, inserting, removal is much more efficient with std::string.

While something like a file buffer only requires a cstring, A text editor requires the most optimal string structure.

Answer 6

Beyond readability, and ensuring another maintainer does not confuse the purpose of the std::string, there is not a lot of difference in function. You could of course consider char*/malloc as well, if efficiency is the only consideration.

One potential issue I can think of:

std::string defaults to storing <char>. If you later needed to handle another type (e.g. unsigned short) you might need to either:

• Create your own typedef std::basic_string<unsigned short> (which moves you away from normal std::string handling)
• Tentatively apply some reinterpret_cast logic in a setter.

With a vector you could simply change the container to a std::vector<unsigned short>.