Fastest way to check if a file exists

Reference:

https://www.it-note.kr/173

stat(2) - 파일의 상태 및 정보를 얻는 함수

 

#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <time.h>


#if 0
struct stat {
    __dev_t     st_dev;     /* Device. */
    __ino_t     st_ino;     /* File serial number */
    __nlink_t   st_nlink;   /* Link count. */
    __mode_t    st_mode;    /* File mode. */
    __uid_t     st_uid;     /* User ID of the file's owner. */
    __gid_t     st_gid;     /* Group ID of the file's group. */
    __dev_t     st_rdev;    /* Device number, if device. */
    __off_t     st_size;    /* Size of file, in bytes. */
    __blksize_t st_blksize; /* Optimal block size for I/O */
    __blkcnt_t  st_blocks;  /* Number 512-byte blocks allocated. */
    /**
     * Nanosecond resolution timestamps are stored in a format
     * equivalent to 'struct timespec'.
     * This is the type used whenever possible
     * but the Unix namespace rules do not allow the identifier 'timespec'
     * to appear in the <sys/stat.h> header.
     * Therefore we have to handle the use of this header
     * in strictly standard-compliant sources sepcial.
     */
    time_t      st_atime;   /* time of last access */
    time_t      st_mtile;   /* time of last modification */
    time_t      st_ctime;   /* time of last status change */
};

int stat(const char *path, struct stat *buf);
#endif


inline bool fs_file_exists(const char *path)
{
    struct stat buffer;
    return stat(path, &buffer) == 0;
}

int example(const char *path)
{
    struct stat sb;
    
    if (stat(path, &sb) == -1)
    {
        // 오류, 상세한 오류 내용은 errno 전역변수에 설정
        perror("stat");
        return errno;
    }
    
    switch (sb.st_mode & S_IFMT)
    {
    case S_IFBLK:  printf("block device\n");     break;
    case S_IFCHR:  printf("character device\n"); break;
    case S_IFDIR:  printf("directory\n");        break;
    case S_IFIFO:  printf("FIFO/pipe\n");        break;
    case S_IFLNK:  printf("symlink\n");          break;
    case S_IFREG:  printf("regular file\n");     break;
    case S_IFSOCK: printf("socket\n");           break;
    default:       printf("unknown?\n");         break;
    }
    
    printf("I-node number:            %ld\n", (long) sb.st_ino);
    printf("Mode:                     %lo (octal)\n", (unsigned long) sb.st_mode);
    printf("Link count:               %ld\n", (long) sb.st_nlink);
    printf("Ownership:                UID=%ld   GID=%ld\n", (long) sb.st_uid, (long) sb.st_gid);
    printf("Preferred I/O block size: %ld bytes\n",         (long) sb.st_blksize);
    printf("File size:                %lld bytes\n",        (long long) sb.st_size);
    printf("Blocks allocated:         %lld\n",              (long long) sb.st_blocks);
    printf("Last status change:       %s", ctime(&sb.st_ctime));
    printf("Last file access:         %s", ctime(&sb.st_atime));
    printf("Last file modification:   %s", ctime(&sb.st_mtime));
    
    return 0;
}

 

#include <iostream>
#include <string>
#include <sys/stat.h>   // stat
#include <errno.h>      // errno, ENOENT, EEXIST
#if defined(_WIN32)
#   include <direct.h>  // _mkdir
#endif


bool fs_file_exists(const std::string& path)
{
#if defined(_WIN32)
    struct _stat info;
    return !_stat(path.c_str(), &info);
#else
    struct stat info;
    return !stat(path.c_str(), &info);
#endif
}

bool fs_dir_exists(const std::string& path)
{
#if defined(_WIN32)
    struct _stat info;
    return _stat(path.c_str(), &info)
        ? false
        : (info.st_mode & _S_IFDIR) != 0;
#else
    struct stat info;
    return stat(path.c_str(), &info)
        ? false
        : (info.st_mode & S_IFDIR) != 0;
#endif
}

bool fs_mkdir(const std::string& path)
{
#if defined(_WIN32)
    int rv = _mkdir(path.c_str());
#else
    mode_t mode = 0755;
    int rv = mkdir(path.c_str(), mode);
#endif

    if (rv)
    {
        switch (errno)
        {
        case ENOENT:
            // parent didn't exist, try to create it
            {
                int pos = path.find_last_of('/');
                if (pos == std::string::npos)
#if defined(_WIN32)
                    pos = path.find_last_of('\\');
                if (pos == std::string::npos)
#endif
                    return false;
                
                if (!fs_mkdir(path.substr(0, pos)))
                    return false;
            }
            // now, try to create again
#if defined(_WIN32)
            return !_mkdir(path.c_str());
#else
            return !mkdir(path.c_str(), mode);
#endif
        case EEXIST:
            // done!
            return fs_dir_exists(path);

        default:
            return false;
        }
    }

    return true;
 }