文件目录相关API

#include
#include
#include

int stat(const char *path, struct stat *buf);
int fstat(int fd, struct stat *buf);
int lstat(const char *path, struct stat *buf);

use struct stat to get file information.
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#include
#include

int utime(const char *filename, const struct utimbuf *times);

#include

int utimes(const char *filename, const struct timeval times[2]);

We know a file(inode) has three time:
--last access time:       last time file content is read.
--last modification time: last time file content is changed.
--last state changed time:last time file properity is changed,
                          that means inode is modified.
struct utimbuf {
    time_t actime;       /* access time */
    time_t modtime;      /* modification time */
};

struct timeval {
    long tv_sec;        /* seconds */
    long tv_usec;       /* microseconds */
};
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#include
int access(const char *pathname, int mode);

R_OK: if can read
W_OK: if can write
X_OK: if can execute
F_OK: if file exists
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#include
#include

mode_t umask(mode_t mask);

change umask to mask.
Note: if a bit in mask is 1, the related bit in file
      access permission bit will be 0.

Common umask:
0002: rwxrwxr-x  only Others can not write.
0022: rwxr-xr-x  Group and Others can not write.
0027: rwxr-x---  Group can not read and Others can not access.
Note:
    This will effect only the process itself.
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#include

int chmod(const char *path, mode_t mode);
int fchmod(int fd, mode_t mode);

Change file access permission.
Note:
    We should get mode via stat() first, then only
    change bits we need.
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#include

int chown(const char *path, uid_t owner, gid_t group);
int fchown(int fd, uid_t owner, gid_t group);
int lchown(const char *path, uid_t owner, gid_t group);

if owner is -1, owner uid of file will not change, and so with
group.
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#include
#include

int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);

changed file size to the specified length.
If file size is shorted than length, '\0'(NULL) will be appended.
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#include

int link(const char *oldpath, const char *newpath);
int unlink(const char *pathname);

create or delete a directory entry to a special file.
unlink doesn't follow symbol link.
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#include

int remove(const char *pathname);

This handles file and directory both. When file it calls unlink(),
when directory, it calls rmdir().
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#include

int rename(const char *oldpath, const char *newpath);

This function doesn't follow symbol link.
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#include

int symlink(const char *oldpath, const char *newpath);
ssize_t readlink(const char *path, char *buf, size_t bufsiz);

create and read a symbol link content.
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#include
#include
int mkdir(const char *pathname, mode_t mode);

#include
int rmdir(const char *pathname);
rmdir() only can remove an empty directory.
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#include
#include

DIR *opendir(const char *name);
DIR *fdopendir(int fd);
int closedir(DIR *dirp);

open and close a directory returning DIR *.
--------------------------------------------------------------
#include
struct dirent *readdir(DIR *dirp);

int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);

struct dirent {
    ino_t          d_ino;       /* inode number */
    off_t          d_off;       /* offset to the next dirent */
    unsigned short d_reclen;    /* length of this record */
    unsigned char  d_type;      /* type of file; not supported
                                   by all file system types */
    char           d_name[256]; /* filename */
};
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#include
#include

void rewinddir(DIR *dirp);
long telldir(DIR *dirp);
void seekdir(DIR *dirp, long offset);

rewinddir() set the current positon to the begging of the directory.
telldir() return the current position in a DIR.
seekdir() set positon where next readdir() will begin to read
          in directory.
----------------------------------------------------------------
#include

int chdir(const char *path);
int fchdir(int fd);

char *getcwd(char *buf, size_t size);
char *getwd(char *buf);
char *get_current_dir_name(void);

chdir() and fchdir() changed process working directory to path.
getcwd() and so on return the current working directory.