When to use std::vector<unsigned char> vs. std::vector<char>

Question

Which of one of these is best suited for managing a character buffer that can be easily converted to std::string and passed to and used ( i.e. read / write ) in C functions

std::vector<unsigned char> 
std::vector<char>

Answer 1

char's signedness depends on the compiler.¹

It can represent a unsigned char or signed char. Which type is used when representing a string is dependent on the compiler - therefore you should use char for portability, and clarity. If that isn't enough, would the less typing needed when writing char convince you? :)

Again, the compiler thinks strings are of type char *, which can be equivalent to unsigned char * or signed char *. If you're going to be working with strings use std::vector<char>.

¹ char is the only type with this behavior.

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References

¹ Is char signed or unsigned by default?

Answer 2

char is more compatible with strings than unsigned char. String literals are char[] and std::string is actually std::basic_string<char>.