Which is better to check if a character exists in a std::string? find or find_first_of?

Question

std::string has two different member functions that do the same thing:

size_type find( CharT ch, size_type pos = 0 ) const noexcept;
size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept;

If I want to check if a character exists in a std::string , which one is preferred in terms of performance?

Answer 1

It doesn't matter. They do the same thing.

Like, literally. libstdc++ just delegates find_first_of(char, size_t) to find(char, size_t) , as does libc++ , and MSVS 2015 too (thanks roalz). There's no reason for any implementation to do otherwise.

I'm not really clear on why that overload of find_first_of even exists; it could just be for symmetry with find (which does something different when you use the other overloads) but to be honest that just seems confusing to me.

Answer 2

They are pretty much identical. But not doing the exact same thing in some specific case and that is depends what std library you are using.

I am using a thing called EWL, (highly likely no 1 is using this anymore) in that library string::find() and string::find_first_of are the same.

But different libraries have different stories. In some library, eg Gnu, C++2a, if you searching an empty string from an empty string, std::find() returns position 0. However std::find_first_of() returns std::string::npos . They are right or wrong depends on the different views you have.

The issue is discussed here .