Unix环境编程笔记3.pdf
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day3
linux 文件系统
1.文件
一切都是文件
- /dev/console 控制台
- /dev/tty 终端 （键盘，显示器。。。。）
- /dev/null 空设备文件(unix 黑洞)
cat /dev/null a.txt
相当于清空a.txt
find 找
open.c
#includestdio.h
#includefcntl.h
#includesys/types.h
#includesys/stat.h
int main()
{
int fd = open( a.txt ,O_RDWR | O_CREAT,0666 );
if(fd == -1)
{
perror( failed );
exit(1);
}
printf( 打开成功fd = %d\n ,fd);
int fd2 = open( b.txt ,O_RDWR | O_CREAT | O_TRUNC /*| O_EXEC*/,0666) ；
if(fd2 == -1)
{
perror( 创建文件失败 ) ；
exit(-1);
}
printf( 创建文件成功fd2 = %d\n ,fd2);
}
读写文件
eg: write.c
#includestdio.h
#includefcntl.h
#includeunistd.h
#includestring.h
#includestdlib.h
int main()
{
int fd = open ( a.txt ,O_WRONLY);
if(fd == -1)
perror( failed ),exit(-1);
int id = 100;
char *name = Daniel ;
double salary = 123456.78
int res = write(fd,id,sizeof(id));
if(res = 0)
perror( faild );
write(fd,name,strlen(name));
write(fd,salary,sizeof(salary));
write(1, hello ,5);//写到显示器
close(fd);
}
eg:read.c
#includestdio.h
#includefcntl.h
#includestdlib.h
#includestring.h
int main()
{
int fd = open( a.txt ,O_READ);
if (-1 == fd)
{
perror( failed );
exit(-1);
}
int id;
int res = read(fd,id,sizeof(id));
if(-1 == res)
perror( 读取失败 );
else
printf( 读取到%d字节数据\n ,res);
//char *name = malloc(100); 也行
char name[100]= {};
read(fd,name,6);
double salary;
read(fd,salary,sizeof(salary));
printf( %d,%s,%lf ,id,name,salary);
close(fd);
}
man read 看read命令
man 2 read / man -s2 read 看read函数
eg: rw.c
#includestdio.h
#includefcntl.h
#includeunistd.h
#includestring.h
#includestdlib.h
struct emp {
int id;
char name[10];
double salary;
};
int main()
{
struct emp e = {100, Daniel , 123456.78};
int fd = open( emp.txt ,O_WRONLY|O_CREAT |O_TRUNC,0666)
if(-1 ==
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