c++判断文件是否存在

 

Fastest way to check if a file exist using standard C++/C++11/C?

https://stackoverflow.com/questions/12774207/fastest-way-to-check-if-a-file-exist-using-standard-c-c11-c

Well I threw together a test program that ran each of these methods 100,000 times, half on files that existed and half on files that didn't.

1. #include

2. #include

3. #include

4.  

5. inline bool exists_test0 (const std::string& name) {

6. ifstream f(name.c_str());

7. return f.good();

8. }

9.  

10. inline bool exists_test1 (const std::string& name) {

11. if (FILE *file = fopen(name.c_str(), "r")) {

12. fclose(file);

13. return true;

14. } else {

15. return false;

16. }

17. }

18.  

19. inline bool exists_test2 (const std::string& name) {

20. return ( access( name.c_str(), F_OK ) != -1 );

21. }

22.  

23. inline bool exists_test3 (const std::string& name) {

24. struct stat buffer;

25. return (stat (name.c_str(), &buffer) == 0);

26. }

Results for total time to run the 100,000 calls averaged over 5 runs,

1. Method exists_test0 (ifstream): **0.485s**

2. Method exists_test1 (FILE fopen): **0.302s**

3. Method exists_test2 (posix access()): **0.202s**

4. Method exists_test3 (posix stat()): **0.134s**

 The stat() function provided the best performance on my system (Linux, compiled with g++), with a standard fopen call being your best bet if you for some reason refuse to use POSIX functions.

Also in Visual Studio 2015: 

1. #include

2.  

3. bool file_exists(std::string fn)

4. {

5. std::experimental::filesystem::exists("helloworld.txt");

6. }

since C++17, only:

std::filesystem::exists("helloworld.txt");

转载于：https://blog.csdn.net/sinat_16577223/article/details/82025089