Running with records-data is a cardinal facet of programming, and effectively figuring out record beingness is important for strong exertion improvement. Figuring out the quickest manner to cheque if a record exists successful C++ tin importantly contact your exertion’s show, particularly once dealing with many record operations. This article explores assorted strategies successful modular C++, C++eleven, C++14, C++17, and C, evaluating their show and highlighting champion practices for optimum record beingness checks.
Utilizing std::filesystem::exists (C++17 and future)
Since C++17, the std::filesystem room supplies the about simple and mostly most well-liked manner to cheque for record beingness. The exists() relation affords a cleanable, level-autarkic resolution.
std::filesystem::exists boasts fantabulous show and readability. It handles assorted record varieties, together with daily records-data, directories, and symbolic hyperlinks. Its transverse-level quality eliminates the demand for OS-circumstantial codification.
Illustration:
see <filesystem> see <iostream> int chief() { std::filesystem::way filePath("my_file.txt"); if (std::filesystem::exists(filePath)) { std::cout << "Record exists!\n"; } other { std::cout << "Record does not be.\n"; } instrument zero; }
C++eleven/14 Options with stat
Earlier C++17, checking record beingness active utilizing level-circumstantial capabilities oregon less-flat scheme calls. 1 communal technique makes use of the stat() scheme call (oregon _stat() connected Home windows). This attack is mostly sooner than utilizing streams for specified beingness checks.
Piece stat() offers record accusation past beingness, it is somewhat much analyzable than std::filesystem::exists.
Illustration:
see <sys/stat.h> // oregon <sys/sorts.h> and <sys/stat.h> connected any methods see <iostream> int chief() { struct stat buffer; if (stat("my_file.txt", &buffer) == zero) { std::cout << "Record exists!\n"; } other { std::cout << "Record does not be.\n"; } instrument zero; }
Utilizing fopen() successful C
Successful C, fopen() is a communal attack to cheque record beingness. Making an attempt to unfastened a record successful publication manner (“r”) volition neglect if the record doesn’t be. This technique is moveable however entails beginning a record grip, which is somewhat little businesslike if you don’t mean to publication the record.
Piece fopen() is elemental, it is mostly slower than stat() for axenic beingness checks, particularly connected Unix-similar techniques.
Illustration:
see <stdio.h> int chief() { Record record = fopen("my_file.txt", "r"); if (record) { fclose(record); // Adjacent the record since we lone checked for beingness. printf("Record exists!\n"); } other { printf("Record does not be.\n"); } instrument zero; }
Show Concerns and Champion Practices
For C++17 and future, std::filesystem::exists is mostly the advisable methodology owed to its readability, portability, and bully show. Successful earlier C++ variations oregon C, stat() is usually quicker than watercourse-based mostly approaches similar fopen() oregon ifstream if lone checking for beingness. Debar repeatedly checking for the aforesaid record’s beingness inside a loop. Cache the consequence for improved ratio.
- Prioritize
std::filesystem::existssuccessful contemporary C++. - Usage
stat()for show successful C oregon older C++ requirements.
See mistake dealing with for much sturdy codification. For illustration, permissions points tin forestall entree equal if a record exists. Scheme calls tin uncover these particulars.
[Infographic placeholder: Evaluating show of antithetic record beingness cheque strategies crossed antithetic working techniques]
Enhance.Filesystem
For pre-C++17 tasks, Increase.Filesystem affords akin performance to std::filesystem, offering a moveable and businesslike resolution.
- See the Enhance.Filesystem room.
- Usage
increase::filesystem::exists().
Larn much astir businesslike record dealing with strategies.FAQ
Q: Is entree() a bully alternate for checking record beingness?
A: Piece entree() tin cheque record beingness and permissions, it’s mostly little businesslike than stat() oregon std::filesystem::exists for purely checking beingness. It’s about utile once you demand to confirm circumstantial entree rights.
Selecting the correct methodology for checking record beingness is important for penning businesslike and strong C++ functions. By knowing the choices disposable successful antithetic C++ requirements and C, and contemplating elements similar portability and show, builders tin brand knowledgeable selections to optimize their record dealing with operations. Retrieve, broad, concise codification coupled with businesslike practices leads to amended package.
- Ever see possible errors, specified arsenic permissions points.
- Cache outcomes to debar redundant checks inside loops.
Research sources similar cppreference.com and Enhance.Filesystem documentation for additional insights. For precocious record scheme operations, see studying astir record watching and notification mechanisms, which supply much businesslike methods to path record adjustments. Record Direction (Home windows) offers much level circumstantial accusation. By mastering these strategies, you tin importantly heighten the show and reliability of your record-dealing with codification.
Question & Answer :
I would similar to discovery the quickest manner to cheque if a record exists successful modular C++eleven, 14, 17, oregon C. I person hundreds of information and earlier doing thing connected them I demand to cheque if each of them be. What tin I compose alternatively of /* Thing */ successful the pursuing relation?
inline bool be(const std::drawstring& sanction) { /* Thing */ }
Fine I threw unneurotic a trial programme that ran all of these strategies a hundred,000 occasions, fractional connected records-data that existed and fractional connected records-data that didn’t.
#see <sys/stat.h> #see <unistd.h> #see <drawstring> #see <fstream> inline bool exists_test0 (const std::drawstring& sanction) { ifstream f(sanction.c_str()); instrument f.bully(); } inline bool exists_test1 (const std::drawstring& sanction) { if (Record *record = fopen(sanction.c_str(), "r")) { fclose(record); instrument actual; } other { instrument mendacious; } } inline bool exists_test2 (const std::drawstring& sanction) { instrument ( entree( sanction.c_str(), F_OK ) != -1 ); } inline bool exists_test3 (const std::drawstring& sanction) { struct stat buffer; instrument (stat (sanction.c_str(), &buffer) == zero); }
Outcomes for entire clip to tally the a hundred,000 calls averaged complete 5 runs,
