std::basic_fstream<CharT,Traits>::is_open
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< cpp | io | basic fstream
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basic_fstream::is_open
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bool is_open() const;
Checks if the file stream has an associated file.
Effectively calls rdbuf()->is_open().
[edit] Parameters
(none)
[edit] Return value
true if the file stream has an associated file, false otherwise.
[edit] Example
Run this code
#include <fstream> #include <iostream> #include <string> int main() { std::string filename = "some_file"; std::fstream fs(filename, std::ios::in); std::cout << std::boolalpha ; std::cout << "fs.is_open() = " << fs.is_open() << '\n'; if (!fs.is_open()) { fs.clear(); fs.open(filename, std::ios::out); std::cout << "fs.is_open() = " << fs.is_open() << '\n'; } }
Possible output:
fs.is_open() = false fs.is_open() = true
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 365 | C++98 | is_open was not declared with const qualifier
|
declared with const qualifier |