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This article is a detailed introduction to "how linux checks whether the file directory exists". The content is detailed, the steps are clear, and the details are properly handled. I hope this article "how linux checks whether the file directory exists" can help you solve your doubts. Let's go deeper and learn new knowledge together with the ideas of the small editor.

View method: 1, using stat series function, if there is, return structure information related to the file;2, using access function, syntax "access(file directory path,F_OK)";3, using oepndir function, if there is, return pointer, if there is no return NULL.

This tutorial operates on Linux 5.9.8 and Dell G3 computers.

linux Check if the file directory exists

1. stat series function

The stat function returns structural information about a file. The stat family of functions has three cases, corresponding to file names, file descriptors, and symbolic link files. stat structure describes the attributes of a file, mainly including file type, file size, and so on. The detailed stat structure is as follows:

struct stat { mode_t st_mode; // file type & mode(permissions) ino_t st_ino; // i-node number(serial number) dev_t st_dev; // device number(filesystem) dev_t st_rdev; // device number for specials files nlink_t st_nlink; // number of links uid_t st_uid; // user ID of owner gid_t st_gid; // group ID of owner off_t st_size; // size in bytes, for regular files time_t st_atime; // time of last access time_t st_mtime; // time of last modification time_t st_ctime; // time of last file status change long st_blksize; // best I/O block size long st_blocks; // number of 512-byte blocks allocated};

We can use stat to get information such as file type and file size. File types are: ordinary file, directory file, block special file, character special file, FIFO, socket and symbolic link. To determine whether a file or directory exists through stat series functions, when the stat function is executed, if the file exists, it is further determined whether the file is a normal file or a directory file.

stat series function error returns-1, error code is stored in errno, errno values are as follows:

ENOENT parameter file_name specified file does not exist ENOTDIR directory in path exists but is not a real directory ELOOP file to be opened has too many symbolic links, the upper limit is 16 symbolic links EFAULT parameter buf is invalid pointer to memory space that does not exist EACCESS file access denied MEM core memory is insufficient ENOMETOOLONG parameter file_name path name is too long

2. Access function

The access function tests access rights by actual user ID and actual group. The prototype function is:

#include int access(const char *pathname, int mode);

Mode value:

F_OK Test file exists

R_OK Test Read Permission

W_OK Test Write Permission

X_OK Test Execution Permission

To correctly determine whether a file exists, use the access function, as shown below:

3. Oepndir function

The opendir function is used to open a file directory. It returns a pointer on success and NULL on error. This is achieved as follows:

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