std::basic_ifstream::open(3)

✨ std::basic_ifstream::open ✨

Bestie, welcome to the std::basic_ifstream::open page from the C++ Standard Libary manual 💖 This is the vibe: opening a file and associating it with your file stream. It's giving file-connection main character energy. 🎀

🌸 NAME 🌸

std::basic_ifstream::open — std::basic_ifstream::open

Okay yes, the NAME section literally says it twice, and we respect the icon behavior. No cap. 💅

🦋 Synopsis 🦋

void open( const char* filename,
           std::ios_base::openmode mode                       (1)
               = std::ios_base::in );
void open( const std::filesystem::path::value_type* filename,
           std::ios_base::openmode mode                       (2)
(since C++17)
               = std::ios_base::in );
void open( const std::string& filename,
           std::ios_base::openmode mode                       (3)
(since C++11)
               = std::ios_base::in );
void open( const std::filesystem::path& filename,
           std::ios_base::openmode mode                       (4)
(since C++17)
               = std::ios_base::in );

Okay so this opens the file with name filename and associates it with the file stream. Slay. 🫶

On success it calls clear(). On failure it calls setstate(failbit). Periodt.

• 1, 2) Effectively calls rdbuf()->open(filename, mode | ios_base::in) (see std::basic_filebuf::open for the details on the effects of that call). Overload (2) is only provided if std::filesystem::path::value_type is not char. (since C++17)
• 3, 4) Effectively calls (1,2) as if by open(filename.c_str(), mode).

🌈 Parameters 🌈

• filename — the name of the file to be opened.
• mode — specifies stream open mode. It is a BitmaskType, and the following constants are defined:
  • app — seek to the end of stream before each write
  • binary — open in binary mode
  • in — open for reading
  • out — open for writing
  • trunc — discard the contents of the stream when opening
  • ate — seek to the end of stream immediately after open
  • noreplace (C++23) — open in exclusive mode

🍓 Return value 🍓

(none) — literally nothing comes back, bestie. 🫶

💀 Example 💀

This section is incomplete.

Reason: no example 😭

😭 Defect reports 😭

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• LWG 22 — Applied to: C++98. Behavior as published: it was unclear how error state changes upon a successful open. Correct behavior: the error state is unchanged.
• LWG 409 — Applied to: C++98. Behavior as published: the error state was unchanged upon a successful open. Correct behavior: it is cleared^[1].

1. ↑ The resolution of LWG issue #22 is overriden.

🔥 See also 🔥

• is_open — checks if the stream has an associated file (public member function)
• close — closes the associated file (public member function)
• open — opens a file and configures it as the associated character sequence (public member function of std::basic_filebuf<CharT,Traits>)

👑 Category 👑

• Todo no example

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mwah 💋 this iconic page came from http://cppreference.com, dated 2024.06.10, and it's the std::basic_ifstream::open(3) page — bye bestie! 🫶