本文介绍了使用标准 C++/C++11、14、17/C 检查文件是否存在的最快方法?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
I would like to find the fastest way to check if a file exist in standard C++11,14,17, or C. I have thousands of files and before doing something on them I need to check if all of them exist. What can I write instead of /* SOMETHING */ in the following function?
inline bool exist(const std::string& name)
{
/* SOMETHING */
}
解决方案
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.
#include <sys/stat.h>
#include <unistd.h>
#include <string>
#include <fstream>
inline bool exists_test0 (const std::string& name) {
ifstream f(name.c_str());
return f.good();
}
inline bool exists_test1 (const std::string& name) {
if (FILE *file = fopen(name.c_str(), "r")) {
fclose(file);
return true;
} else {
return false;
}
}
inline bool exists_test2 (const std::string& name) {
return ( access( name.c_str(), F_OK ) != -1 );
}
inline bool exists_test3 (const std::string& name) {
struct stat buffer;
return (stat (name.c_str(), &buffer) == 0);
}
Results for total time to run the 100,000 calls averaged over 5 runs,
| Method | Time |
|---|---|
exists_test0 (ifstream) |
0.485s |
exists_test1 (FILE fopen) |
0.302s |
exists_test2 (posix access()) |
0.202s |
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.
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