一、头文件
#include <unistd.h>
二、函数原型
int unlink(const char *pathname);
三、函数介绍
unlink()函数功能即为删除文件。执行unlink()函数会删除所给参数指定的文件。
注意：
执行unlink()函数并不一定会真正的删除文件，它先会检查文件系统中此文件的连接数是否为
1，如果不是1说明此文件还有其他链接对象，因此只对此文件的连接数进行减1操作。若连接数为1，并且在此时没有任何进程打开该文件，此内容才会真正地被删除掉。在有进程打开此文件的情况下，则暂时不会删除，直到所有打开该文件的进程都结束时文件就会被删除。
返回值：成功返回0，失败返回 -1
四、代码示例
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <assert.h>
int main(int argc, const char * argv[]) {
int fd = open("test.txt", O_RDWR | O_TRUNC | O_CREAT, 0664);
assert(fd != -1);
if (unlink("test.txt") < 0) {
printf("unlink errpr!\n");
}
char buff[128] = {0};
write(fd, "hello world!", 12);
if (lseek(fd, 0, SEEK_SET) == -1) {
printf("lseek error!\n");
}
read(fd, buff, 12);
printf("%s\n", buff);
return 0;
}
五、运行结果
hello world!
Program ended with exit code: 0
从结果可以得出，在文件打开的情况下unlink()并不会立即删除，并且对文件依然可以进行读写操作，在进程结束之后文件就会被删除掉！
六、函数说明
UNLINK(2) BSD System Calls Manual UNLINK(2)
NAME
unlink, unlinkat -- remove directory entry
SYNOPSIS
#include <unistd.h>
int
unlink(const char *path);
int
unlinkat(int fd, const char *path, int flag);
DESCRIPTION
The unlink() function removes the link named by path from its direc-
tory and decrements the link count of the file which was referenced
by the link. If that decrement reduces the link count of the file
to zero, and no process has the file open, then all resources asso-
ciated with the file are reclaimed. If one or more process have the
file open when the last link is removed, the link is removed, but
the removal of the file is delayed until all references to it have
been closed.
The unlinkat() system call is equivalent to unlink() or rmdir()
except in the case where path specifies a relative path. In this
case the directory entry to be removed is determined relative to the
directory associated with the file descriptor fd instead of the cur-
rent working directory.
The values for flag are constructed by a bitwise-inclusive OR of
flags from the following list, defined in <fcntl.h>:
AT_REMOVEDIR
Remove the directory entry specified by fd and path as a
directory, not a normal file.
If unlinkat() is passed the special value AT_FDCWD in the fd parame-
ter, the current working directory is used and the behavior is iden-
tical to a call to unlink or rmdir respectively, depending on
whether or not the AT_REMOVEDIR bit is set in flag.
RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned and errno is set to indicate the error.
ERRORS
The unlink() system call will fail if:
[EACCES] Search permission is denied for a component of
the path prefix.
[EACCES] Write permission is denied on the directory con-
taining the link to be removed.
[EBUSY] The entry to be unlinked is the mount point for a
mounted file system.
[EBUSY] The file named by the path argument cannot be
unlinked because it is being used by the system
or by another process.
[EFAULT] Path points outside the process's allocated
address space.
[EIO] An I/O error occurs while deleting the directory
entry or deallocating the inode.
[ELOOP] Too many symbolic links are encountered in trans-
lating the pathname. This is taken to be indica-
tive of a looping symbolic link.
[ENAMETOOLONG] A component of a pathname exceeds {NAME_MAX}
characters, or an entire path name exceeds
{PATH_MAX} characters (possibly as a result of
expanding a symlink).
[ENOENT] The named file does not exist.
[ENOTDIR] A component of the path prefix is not a direc-
tory.
[EPERM] The named file is a directory and the effective
user ID of the process is not the super-user.
[EPERM] The directory containing the file is marked
sticky, and neither the containing directory nor
the file to be removed are owned by the effective
user ID.
[EROFS] The named file resides on a read-only file sys-
tem.
In addition to the errors returned by the unlink(), the unlinkat()
may fail if:
[EBADF] The path argument does not specify an absolute
path and the fd argument is neither AT_FDCWD nor
a valid file descriptor open for searching.
[ENOTEMPTY] The flag parameter has the AT_REMOVEDIR bit set
and the path argument names a directory that is
not an empty directory, or there are hard links
to the directory other than dot or a single entry
in dot-dot.
[ENOTDIR] The flag parameter has the AT_REMOVEDIR bit set
and path does not name a directory.
[EINVAL] The value of the flag argument is not valid.
[ENOTDIR] The path argument is not an absolute path and fd
is neither AT_FDCWD nor a file descriptor associ-
ated with a directory.
SEE ALSO
close(2), link(2), rmdir(2), symlink(7)
STANDARDS
The unlinkat() system call is expected to conform to POSIX.1-2008 .
HISTORY
An unlink() function call appeared in Version 6 AT&T UNIX. The
unlinkat() system call appeared in OS X 10.10
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution
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