使用标准C ++ / C ++ 11 / C检查文件是否存在最快的方法？ [英] Fastest way to check if a file exist using standard C++/C++11/C?

问题描述

我想找到最快的方式来检查文件是否存在于标准C ++ 11，C ++或C中。我有数千个文件，在对其进行处理之前，我需要检查它们是否存在。在以下功能中可以写入什么，而不是 / * SOMETHING * / ？

I would like to find the fastest way to check if a file exist in standard C++11, C++, 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

程序运行这些方法100,000次，一半存在文件，一半在没有的文件上。

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>

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); 
}

在5次运行中平均运行100,000次通话的总时间的结果

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

Method exists_test0 (ifstream): **0.485s**
Method exists_test1 (FILE fopen): **0.302s**
Method exists_test2 (posix access()): **0.202s**
Method exists_test3 (posix stat()): **0.134s**

stat（）函数在我的系统上提供了最好的性能（Linux，使用g ++编译），标准的fopen调用是您最好的选择，有些原因拒绝使用POSIX功能。

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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