Open () function

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int open (const char *pathname, int flags);
int open (const char *pathname, int flags, mode_t mode);

For the Open function, the third parameter is used only when a new file is created (that is, when o_creat is used) to specify the access bit (access permission bits) for the file.

Pathname is a POSIX pathname (such as/home/user/a.cpp) to open/create a file;

Flags are used to specify the open/create mode of a file, which can be composed of logical bits or logic by the following constants (defined by Fcntl.h).

O_RDONLY只读模式 O_WRONLY只写模式 O_RDWR读写模式 The above three flags are mutually exclusive, that is, cannot be used simultaneously, but can be used with the following flags to take advantage of or (|) operator combinations. O_CREAT若欲打开的文件不存在则自动建立该文件。 O_EXCL如果O_CREAT也被设置，此指令会去检查文件是否存在。文件若不存在则建立该文件，否则将导致打开文件错误。此外，若O_CREAT与O_EXCL同时设置，并且欲打开的文件为符      号连接，则会打开文件失败。 O_NOCTTY如果欲打开的文件为终端机设备时，则不会将该终端机当成进程控制终端机。 O_TRUNC若文件存在并且以可写的方式打开时，此标志位会令文件长度清为0，而原来存于该文件的资料也会消失。 O_APPEND当读写文件时会从文件尾开始移动，也就是所写入的数据会以附加的方式加入到文件后面。 O_NONBLOCK以不可阻断的方式打开文件，也就是无论有无数据读取或等待，都会立即返回进程之中。 O_NDELAY同O_NONBLOCK。 O_SYNC以同步的方式打开文件。 O_NOFOLLOW如果参数pathname所指的文件为一符号连接，则会令打开文件失败。 O_DIRECTORY如果参数pathname所指的文件并非为一目录，则会令打开文件失败。parameter ModeThis is special for Linux2.2. flag BitTo avoid some system security issues. The parameter mode has the following combinations, which will only take effect when a new file is created, and the permissions of the real file will be affected by the umask value, so the file permission should be (Mode-umaks). Example:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
int main (void)
{

Char a[] = {"Abc.txt"};
int fd = open (A, o_rdonly);

if (fd = =-1)
{
printf ("%s\n", Strerror (errno));//Determine if Open is successful
}
Else
{
printf ("%d\n", FD);
Close (FD);//When you are finished, remember to close the file
}

return exit_success;
}

Open () function