使用标准 C++/C++11,14,17/C 检查文件是否存在的最快方法?

2021-12-02 00:00:00 file c stream c++

我想找到检查标准 C++11、14、17 或 C 中是否存在文件的最快方法.我有数千个文件，在对它们执行某些操作之前，我需要检查是否所有文件都存在存在.我可以在下面的函数中写什么来代替 /* SOMETHING */ ?

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 */
}

推荐答案

好吧，我拼凑了一个测试程序，该程序运行这些方法中的每一种 100,000 次，一半在存在的文件上，一半在不存在的文件上.

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); 
}

运行 100,000 次调用的总时间平均超过 5 次运行的结果，

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

<头>
方法时间
exists_test0 (ifstream)0.485s
exists_test1 (FILE fopen)0.302s
exists_test2 (posix access())0.202s
exists_test3 (posix stat())0.134s
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

stat() 函数在我的系统(Linux，使用 g++ 编译)上提供了最佳性能，标准的 fopen 调用是如果您出于某种原因拒绝使用 POSIX 函数，那么您最好的选择.

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.

相关文章