PR_Open 编辑

Opens a file for reading, writing, or both. Also used to create a file.

Syntax

#include <prio.h>

/wiki/en-US/docs/Mozilla/Projects/NSPR/Reference/PRFileDesc* PR_Open(
  const char *name,
  /wiki/en-US/docs/Mozilla/Projects/NSPR/Reference/PRIntn flags,
  /wiki/en-US/docs/Mozilla/Projects/NSPR/Reference/PRIntn mode);

Parameters

The function has the following parameters:

name

The pathname of the file to be opened.

flags

The file status flags define how the file is accessed. It is a bitwise OR of the following bit flags. In most cases, only one of the first three flags may be used. If the flags parameter does not include any of the first three flags (PR_RDONLY, PR_WRONLY, or PR_RDWR), the open file can't be read or written, which is not useful.

NOTE: The constants PR_RDWR and friends are not in any interface (bug 433295). Thus they cannot be used in JavaScript, you have to use the octal constants (see File I/O Snippets).

Name	Value	Description
PR_RDONLY	0x01	Open for reading only.
PR_WRONLY	0x02	Open for writing only.
PR_RDWR	0x04	Open for reading and writing.
PR_CREATE_FILE	0x08	If the file does not exist, the file is created. If the file exists, this flag has no effect.
PR_APPEND	0x10	The file pointer is set to the end of the file prior to each write.
PR_TRUNCATE	0x20	If the file exists, its length is truncated to 0.
PR_SYNC	0x40	If set, each write will wait for both the file data and file status to be physically updated.
PR_EXCL	0x80	With PR_CREATE_FILE, if the file does not exist, the file is created. If the file already exists, no action and NULL is returned.

mode

When PR_CREATE_FILE flag is set and the file is created, these flags define the access permission bits of the newly created file. This feature is currently only applicable on Unix platforms. It is ignored by any other platform but it may apply to other platforms in the future. Possible values of the mode parameter are listed in the table below.

Name	Value	Description
PR_IRWXU	0700	read, write, execute/search by owner.
PR_IRUSR	0400	read permission, owner.
PR_IWUSR	0200	write permission, owner.
PR_IXUSR	0100	execute/search permission, owner.
PR_IRWXG	0070	read, write, execute/search by group
PR_IRGRP	0040	read permission, group
PR_IWGRP	0020	write permission, group
PR_IXGRP	0010	execute/search permission, group
PR_IRWXO	0007	read, write, execute/search by others
PR_IROTH	0004	read permission, others
PR_IWOTH	0002	write permission, others
PR_IXOTH	0001	execute/search permission, others

Returns

The function returns one of the following values:

• If the file is successfully opened, a pointer to a dynamically allocated /wiki/en-US/docs/Mozilla/Projects/NSPR/Reference/PRFileDesc for the newly opened file. The /wiki/en-US/docs/Mozilla/Projects/NSPR/Reference/PRFileDesc should be freed by calling /wiki/en-US/docs/Mozilla/Projects/NSPR/Reference/PR_Close.
• If the file was not opened successfully, a NULL pointer.

Description

PR_Open creates a file descriptor (/wiki/en-US/docs/Mozilla/Projects/NSPR/Reference/PRFileDesc) for the file with the pathname name and sets the file status flags of the file descriptor according to the value of flags. If a new file is created as a result of the PR_Open call, its file mode bits are set according to the mode parameter.