Difference between std::ifstream(std::basic_ifstream<char>) and std::basic_ifstream<uint8_t>

[knorrfix]

Channel

Probably "C++Weekly" in my opinion this is not really intuitive and may surprise others as well.

Topics

I have found some behavior of std::basic_ifstream that surprised me, std::basic_ifstream returned in the following case the expected values, but std::basic_ifstream<uint8_t> did return only zeros: https://godbolt.org/z/9Tasccf96, what is happening here? As a user that doesn't use streams regularly this is very surprising to me.

What is the difference between std::ifstream aka. std::basic_ifstream and the other possible template instantiations, when can and should you use std::ifstream and when do you need to use one of the other template instantiations like (u)int8_t, (u)int16_t, ...

Length

I think the episode should be between 5 and 10 Minutes, depending on if there are some other interesting things to know in

[LB--]

char, signed char, and unsigned char are three distinct types, where char can be signed or unsigned depending on platform and compiler settings. uint8_t is likely unsigned char, which is always different from char even if char is unsigned on your platform. Many standard library types that work with text only know how to work with char/wchar_t/etc, and require you to specialize customization points to work with other types. In your code, the read operation fails at runtime due to the missing information on how to handle unsigned char: https://godbolt.org/z/EWjcKaxaG - as for why this is not a compile time error, I guess the IOStreams stuff in the standard library is so old it predates tricks and enforcement of making wrong code fail to compile.