APUE_chapter3 文件IO

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>// 对POSIX操作系统API的访问功能的头文件名称
// open lseek open write close
int main(int argc , char* argv[]){// 3.1 - 3.8
int fd = open (argv[1], O_RDWR | O_APPEND | O_CLOEXEC | O_CREAT); //  open
if (fd  == -1)
printf ("fail to open file:%s \n", argv[1]);
else{
printf ("succeed to open file:%s \n", argv[1]);

// 若成功返回新的文件偏移量，出错返回-1；
off_t curpos = lseek (fd, 0, SEEK_CUR);

char* buf = (char*)malloc(100 * sizeof(char));
// 文件尾返回0，出错返回-1
while (read (fd, buf, 100) > 0){
printf ("succeed to read the file : %s \n", buf);
}
char output[] = "hello world!\n";
if ( write (fd, output, strlen(output)) == -1)
printf ("succeed to write the file:%s \n", argv[1]);
if (!close (fd)) // return 0 when succeed                                      //  close
printf ("succeed to close file:%s \n", argv[1]);
else
printf ("fail to close file:%s \n", argv[1]);
}
return 0;
}

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>// 对POSIX操作系统API的访问功能的头文件名称
// fsync fdatasync
int main(int argc , char* argv[]){ // 3.13
int fd = open (argv[1], O_RDWR | O_APPEND | O_CLOEXEC | O_CREAT);
char output[] = "hello world!\n";
time_t start_time = time(NULL);
for (int i = 0; i < 10000000; ++i)
write(fd, output, strlen(output));
printf ("%d\n", time(NULL) - start_time); // 5s
close(fd);

fd = open (argv[1], O_RDWR | O_TRUNC | O_CLOEXEC | O_CREAT);
fdatasync(fd);
for (int i = 0; i < 10000000; ++i)
write(fd, output, strlen(output)); //10s
printf ("%d\n", time(NULL) - start_time);
close(fd);

fd = open (argv[1], O_RDWR | O_TRUNC | O_CLOEXEC | O_CREAT);
fsync(fd);
for (int i = 0; i < 10000000; ++i)
write(fd, output, strlen(output)); // 15s
printf ("%d\n", time(NULL) - start_time);
close(fd);

printf("finished");
return 0;
}

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
// fctnl函数 : 改变已经打开文件的属性,错误返回 - 1
int main(int argc, char* argv[]){ //3.14
int fd = open (argv[1], O_RDWR | O_APPEND | O_CLOEXEC | O_CREAT); // O_SYNC 可以指定
printf( "%d\n", fcntl (fd, F_GETFD, 0)); // return O_CLOEXEC

int file_state_flag = fcntl(fd, F_GETFL, 0);
if ( file_state_flag < 0){
printf ("fctnl error for fd: %s \n", argv[1]);
exit(1);
}
else{
print_file_state_flag(file_state_flag);
// 无法设置O_SYNC, 但显示成功设置
if ( fcntl (fd, F_SETFL,  file_state_flag | O_NONBLOCK | O_SYNC) < 0 ){
printf ("fail to set the file state\n");
exit(1);
}
else{ // 成功返回0
print_file_state_flag( fcntl(fd, F_GETFL, 0));
}
}
close (fd);
return 0;
}
void print_file_state_flag(int file_state_flag){
switch ( file_state_flag & O_ACCMODE){ // O_ACCMODE = 3;
case O_RDONLY:
printf ("read only \n");
break;
case O_WRONLY:
printf("write only \n");
break;
case O_RDWR:
printf("read and write \n");
break;
default:
printf ("unknown access mode\n");
}
if ( file_state_flag  & O_APPEND)
printf ("append\n");
if ( file_state_flag & O_NONBLOCK)
printf ("nonblock\n");
if ( file_state_flag & O_SYNC)
printf ("sync\n");
}
void change_file_state_flag(int fd, int flag){ // set or clear
int new_flag = fcntl(fd, F_GETFL, 0);
new_flag |= flag;  // set
//new_flag &= ~flag;  //clear
if (fcntl(fd, F_SETFL, new_flag) < 0){
printf ("fail to set the file state flag\n");
exit(1);
}
}