有了上篇关于ac的实现，对于这个last的实现过程就是很简单了。首先 man 1 last。
描述中写着last looks through the file wtmp (which records all logins/logouts) and prints information about connect times of users.也就是还是读的wtmp这个文件。
所以代码的实现就很简单了，我参照大犇的ac写了个last。代码如下：
#include <stdio.h> #include <utmp.h> #include <string.h> #include <sys/utsname.h> struct acc{ short ut_type; char ut_name[UT_NAMESIZE]; char ut_line[UT_LINESIZE]; char ut_host[UT_HOSTSIZE]; int32_t login_sec; int32_t logout_sec; /* 0 still in, -1 down*/ int diff; /* logout_sec - login_sec */ } record[1024]; static int num_rd; #define STILL_IN 0 #define DOWN -1 void output_ans(void); char *format_time(int t); int main(int ac, char *av[]) { struct utmp *utbufp, *utbufp_next(void); int utmp_open(char *filename); void utmp_close(void); int i; if(utmp_open(WTMP_FILE) == -1){ perror(WTMP_FILE); exit(1); } num_rd = 0; while(utbufp = utmp_next()){ switch(utbufp->ut_type){ case USER_PROCESS: case BOOT_TIME: record[num_rd].login_sec = utbufp->ut_time; record[num_rd].logout_sec = STILL_IN; record[num_rd].ut_type = utbufp->ut_type; strcpy(record[num_rd].ut_name, utbufp->ut_name); strcpy(record[num_rd].ut_line, utbufp->ut_type == USER_PROCESS ? utbufp->ut_line : "system"); strcpy(record[num_rd].ut_host, utbufp->ut_host); ++num_rd; break; case DEAD_PROCESS: for(i = 0; i < num_rd; ++i){ if(record[i].ut_type == USER_PROCESS && !strcmp(record[i].ut_line, utbufp->ut_line)){ record[i].logout_sec = utbufp->ut_time; record[i].ut_type = DEAD_PROCESS; record[i].diff = record[i].logout_sec - record[i].login_sec; break; } } break; case RUN_LVL: /* utbufp->ut_time > record[num_rd - 1].login_sec guarantee that can record boot time normally */ if(!strcmp("runlevel", utbufp->ut_name) && utbufp->ut_time > record[num_rd - 1].login_sec) for(i = 0; i < num_rd; ++i) if(record[i].ut_type == USER_PROCESS || record[i].ut_type == BOOT_TIME){ record[i].logout_sec = utbufp->ut_time; record[i].diff = record[i].logout_sec - record[i].login_sec; if(record[i].ut_type == USER_PROCESS) record[i].logout_sec = DOWN; /* quit because shutdown */ record[i].ut_type = DEAD_PROCESS; } break; } } output_ans(); utmp_close(); return 0; } void output_ans(void) { int i; time_t now_t = time(NULL); struct utsname buf; uname(&buf); for(i = num_rd - 1; i >= 0; --i){ if(record[i].ut_type == BOOT_TIME){ record[i].logout_sec = (int32_t)now_t; record[i].diff = record[i].logout_sec - record[i].login_sec; } printf("%-8.8s ", record[i].ut_name); printf("%-6.6s ", record[i].ut_line); if(!strcmp(record[i].ut_line, "system")){ printf("%-5.5s ", "boot"); printf("%-16.16s ", buf.release); /* 4.2.0-27-generic */ }else{ printf("%-5.5s ", ""); printf("%-16.16s ", record[i].ut_host); } printf("%-16.16s ", asctime(localtime(&record[i].login_sec))); switch(record[i].logout_sec){ case STILL_IN: printf(" %-5.5s ", "still"); break; case DOWN: printf("- %-5.5s ", "down"); break; default: printf("- %-5.5s ", asctime(localtime(&record[i].logout_sec)) + 11); break; } if(record[i].ut_type == USER_PROCESS) printf("logged in\n"); else printf(" (%s)\n", format_time(record[i].diff)); } } char *format_time(int t) { static char buf[10]; int h; int m; t /= 60; m = t % 60; h = t / 60; sprintf(buf, "%.2d:%.2d", h, m); return buf; }用到的utmp缓存：
#include <utmp.h> #include <unistd.h> #include <fcntl.h> #define BUFMAX 10 #define UTSIZ sizeof(struct utmp) static int fd = -1; static int utCur; static int utSum; struct utmp utmpBuf[BUFMAX]; struct utmp *utmp_reload(void); struct utmp *utmp_next(void) { if(fd == -1) return NULL; if(utCur == utSum) return utmp_reload(); return &utmpBuf[utCur++]; } struct utmp *utmp_reload(void) { int bytes_read = read(fd, utmpBuf, sizeof(utmpBuf)); utCur = 0; utSum = bytes_read / UTSIZ; return utSum > 0 ? &utmpBuf[utCur++] : NULL; } int utmp_open(char *filename) { utCur = utSum = 0; return fd = open(filename, O_RDONLY); } void utmp_close(void) { if(fd != -1) close(fd); }效果：
