c++-standard-library – Tarik Billa

Why does `std::string::find()` not return the end iterator on failures?

January 8, 2024 by Tarik

To begin with, the std::string interface is well known to be bloated and inconsistent, see Herb Sutter’s Gotw84 on this topic. But nevertheless, there is a reasoning behind std::string::find returning an index: std::string::substr. This convenience member function operates on indices, e.g. const std::string src = “https://stackoverflow.com/questions/58430288/abcdefghijk”; std::cout << src.substr(2, 5) << “\n”; You could implement … Read more

How similar are Boost.Filesystem and the C++ standard filesystem library?

January 8, 2024 by Tarik

There are a number of differences. Some were, I believe, Boost changes that were never propagated. For example, there is no path.filename_is_dot() query (as discussed below, it would be less useful in std::filesystem anyway). There was also a good bit of late-breaking news on this front: Support for non-POSIX-like filesystems: Specify whether a string is … Read more

Why does pow(n,2) return 24 when n=5, with my compiler and OS?

January 7, 2024 by Tarik

Here is what may be happening here. You should be able to confirm this by looking at your compiler’s implementation of the pow function: Assuming you have the correct #include’s, (all the previous answers and comments about this are correct — don’t take the #include files for granted), the prototype for the standard pow function … Read more

Get index by type in std::variant

January 2, 2024 by Tarik

Update a few years later: My answer here may be a cool answer, but this is the correct one. That is how I would solve this problem today. We could take advantage of the fact that index() almost already does the right thing. We can’t arbitrarily create instances of various types – we wouldn’t know … Read more

Should reading negative into unsigned fail via std::cin (gcc, clang disagree)?

December 28, 2023 by Tarik

I think that both are wrong in C++171 and that the expected output should be: 4294967295 0 While the returned value is correct for the latest versions of both compilers, I think that the ios_base::failbit should be set, but I also think there is a confusion about the notion of field to be converted in … Read more

Why is std::byte an enum class instead of a class?

December 27, 2023 by Tarik

A class with an unsigned char member would not be required by the standard to be the same size or alignment as unsigned char. Whereas the standard requires that enumerations be the same size and alignment as their underlying types. Now, the standard could have simply declared that it is a class type with no … Read more

Is this correct usage of C++ ‘move’ semantics? [duplicate]

December 12, 2023 by Tarik

A reference is still a reference. In the same way you cannot return a reference to a local in C++03 (or you get UB), you can’t in C++0x. You’ll end up with a reference to a dead object; it just happens to be an rvalue reference. So this is wrong: std::vector<T>&& doSomething() const { std::vector<T> … Read more

Gnu C++ macro __cplusplus standard conform?

December 6, 2023 by Tarik

This was fixed about a month ago (for gcc 4.7.0). The bug report makes for an interesting read: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=1773

Is there a pure virtual function in the C++ Standard Library?

December 2, 2023 by Tarik

[syserr.errcat.overview] has std::error_category class error_category { virtual const char* name() const noexcept = 0; virtual string message(int ev) const = 0; }; There are no others in C++14.

How to compare the signature of two functions?

September 18, 2023 by Tarik

Essentially you want to check if types of two functions are the same: std::is_same_v<decltype(funA), decltype(funB)> I wouldn’t call this ‘comparing signatures’, as, if I remember correctly, return type is not a part of a signature (because it doesn’t affect overload resolution).