1. 系统api与库函数的关系
man 2 open
1.1 open
1.2 read/write
实现cat功能
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h> int main(int argc, char *argv[])
{ if (argc != )
{
printf("./a.out filename\n");
return -;
} int fd = open(argv[], O_RDONLY); //读，输出到屏幕
char buff[];
int ret = ;
while (ret = read(fd, buff, sizeof(buff)))
{
write(STDOUT_FILENO, buff, ret); } close(fd); return ;
}
1.3 lseek
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h> int main(int argc, char *argv[])
{ if (argc != )
{
printf("./a.out filename\n");
return -;
} int fd = open(argv[], O_RDWR|O_CREAT, ); write(fd, "helloword", );
//文件读写的位置此时到末尾
//需要移动读写的位置
lseek(fd, , SEEK_SET); char buf[] = {};
int ret = read(fd, buf, sizeof(buf)); if (ret)
{
write(STDOUT_FILENO, buf, ret);
} close(fd); return ;
}
计算大小
int fd = open(argv[], O_WRONLY);
int ret = lseek(fd, , SEEK_END);
printf("file size is %d\n", ret);
close(fd);
拓展文件
//1. open
int fd = open(argv[], O_WRONLY|O_CREAT, ); int ret = lseek(fd, , SEEK_END); printf("file size is %d\n", ret); //需要至少写一次，否则不能保存
write(fd, "a", ); close(fd);
1.4 阻塞
- read函数在读设备或者的读管道，或者读网络的时候。
- 输入输出设备对应 /dev/tty
int fd = open("/dev/tty", O_RDWR|O_CREAT|O_NONBLOCK);
1.5 fcntl函数--设置非阻塞
#include <unistd.h>
#include <fcntl.h> int fcntl(int fd, int cmd, ... /* arg */ );
int flags = fcntl(fd, F_GETFL);
flags |= O_NONBLOCK;