1.使用create建立文件:
#include#include #include #include int main() { int res = creat("./file.txt", 0700); if (res == -1) { perror("Create File Error!"); } else { printf("Create OK!\n"); } return 0;}
2.从输入到输出:
// 从stdin到sdtout#include#include int main (int argc, char *argv[]){ int c; while ((c = getchar()) != EOF) { putchar(c); } return 0;}
3.简单实现who命令:
#include#include #include #include #include #include #define SHOWHOSTvoid show_info(struct utmp* user_record);void login_time(long *num_time);void show_info(struct utmp* user_record) { if (user_record->ut_type != USER_PROCESS) { return ; } printf("-------------------\n"); printf("User Name is: %10s\n", user_record->ut_name); printf("User CMD is: %10s\n", user_record->ut_line); login_time(&(user_record->ut_time)); #ifdef SHOWHOST printf("User Host is: %s\n", user_record->ut_host); #endif printf("\n");}void login_time(long *num_time) { char *timestr; timestr = ctime(num_time); printf("User login time is: %30s\n", timestr);}int main() { struct utmp current_record; int record_len = sizeof(current_record); int user_info_fd = -1; // user info in the utmp if ((user_info_fd = open(UTMP_FILE, O_RDONLY)) == -1) { perror("read file error!"); exit(1); } while (record_len == (read(user_info_fd, ¤t_record, record_len))) { show_info(¤t_record); } close(user_info_fd); return 0;}
4.简单实现cp命令:
#include#include #include #include #define BUFFERSIZE 4096#define FILEMODE 0700 // 111 000 000 User all pervoid opps(char *file, char* argv);void opps(char *file, char* argv) { fprintf(stderr, "Error : %s", file); perror(argv); exit(1);}int main(int argc, char* argv[]) { int in_fd = -1; int out_fd = -1; int n_chars = -1; char buf[BUFFERSIZE]; if (argc != 3) { fprintf(stderr, "Usage: cp source dest\n"); exit(1); } if ((in_fd = open(argv[1], O_RDONLY)) == -1) { opps("Open First File Error", argv[1]); } if ((out_fd = creat(argv[2], FILEMODE)) == -1) { opps("Creat Second File Error", argv[2]); } while ((n_chars = read(in_fd, buf, BUFFERSIZE)) > 0) { if (n_chars != write(out_fd, buf, n_chars)) { opps("Write Error!", argv[2]); } } if (-1 == n_chars) { opps("Read Error!", argv[1]); } if (close(in_fd) == -1 || close(out_fd)) { opps("Close Error!", " "); } return 0;}
5.使用不同缓冲区的cp实验:
使用python得到5M多的一个文件
#!/usr/bin/env python#-*- coding:utf-8 -*-fd = open("./data", "w+");for i in xrange(500000): fd.writelines("hello world!")fd.close() 分别使用1 4026 20000做为buf的cp实验:
使用缓冲区的利弊:
利：
1. 提高磁盘I/O效率2. 优化磁盘的写操作利弊:如果不及时写入磁盘，会导致数据丢失。可以使用sync 将缓冲区数据写入磁盘 通过
man sync 来查看详细说明6.一个进程多次打开一个文件：
#include#include #include #include #include int main() { int read_fd = open("./data", O_RDONLY); int write_fd = open("./data", O_WRONLY); int read_again_fd = open("./data", O_RDWR); char buf[1024]; read(read_fd, buf, 1024); buf[strlen(buf) - 1] = '\0'; puts(buf); close(read_fd); char str[100] = "testing 123..."; write(write_fd, str, strlen(str)); close(write_fd); buf[0] = '\0'; read(read_again_fd, buf, 1024); buf[strlen(buf) - 1] = '\0'; puts(buf); close(read_again_fd); return 0;}
每次都从最开始读取。