进程通信笔记
来自apue fig15.5 fig 15.6
#include "apue.h"intmain(void){ int n; int fd[2]; pid_t pid; char line[MAXLINE]; if (pipe(fd) < 0) err_sys("pipe error"); if ((pid = fork()) < 0) { err_sys("fork error"); } else if (pid > 0) { /* parent */ close(fd[0]); write(fd[1], "hello world\n", 12); } else { /* child */ close(fd[1]); n = read(fd[0], line, MAXLINE); write(STDOUT_FILENO, line, n); } exit(0);}
#include "apue.h"#include <sys/wait.h>#defineDEF_PAGER"/bin/more"/* default pager program */intmain(int argc, char *argv[]){intn;intfd[2];pid_tpid;char*pager, *argv0;charline[MAXLINE];FILE*fp;if (argc != 2)err_quit("usage: a.out <pathname>");if ((fp = fopen(argv[1], "r")) == NULL)err_sys("can't open %s", argv[1]);if (pipe(fd) < 0)err_sys("pipe error");if ((pid = fork()) < 0) {err_sys("fork error");} else if (pid > 0) {/* parent */close(fd[0]);/* close read end *//* parent copies argv[1] to pipe */while (fgets(line, MAXLINE, fp) != NULL) {n = strlen(line);if (write(fd[1], line, n) != n)err_sys("write error to pipe");}if (ferror(fp))err_sys("fgets error");close(fd[1]);/* close write end of pipe for reader */if (waitpid(pid, NULL, 0) < 0)err_sys("waitpid error");exit(0);} else {/* child */close(fd[1]);/* close write end */if (fd[0] != STDIN_FILENO) {if (dup2(fd[0], STDIN_FILENO) != STDIN_FILENO)err_sys("dup2 error to stdin");close(fd[0]);/* don't need this after dup2 */}/* get arguments for execl() */if ((pager = getenv("PAGER")) == NULL)pager = DEF_PAGER;if ((argv0 = strrchr(pager, '/')) != NULL)argv0++;/* step past rightmost slash */elseargv0 = pager;/* no slash in pager */if (execl(pager, argv0, (char *)0) < 0)err_sys("execl error for %s", pager);}exit(0);}#include "apue.h"#include <sys/wait.h>#define PAGER "${PAGER:-more}" /* environment variable, or default */intmain(int argc, char *argv[]){ char line[MAXLINE]; FILE *fpin, *fpout; if (argc != 2) err_quit("usage: a.out <pathname>"); if ((fpin = fopen(argv[1], "r")) == NULL) err_sys("can't open %s", argv[1]); if ((fpout = popen(PAGER, "w")) == NULL) err_sys("popen error"); /* copy argv[1] to pager */ while (fgets(line, MAXLINE, fpin) != NULL) { if (fputs(line, fpout) == EOF) err_sys("fputs error to pipe"); } if (ferror(fpin)) err_sys("fgets error"); if (pclose(fpout) == -1) err_sys("pclose error"); exit(0);}