历程通信笔记
进程通信笔记
来自apue fig15.5 fig 15.6
调用/bin/more
popen和pclose函数 fig15.11
来自apue fig15.5 fig 15.6
#include "apue.h" int main(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); }
调用/bin/more
#include "apue.h" #include <sys/wait.h> #define DEF_PAGER "/bin/more" /* default pager program */ int main(int argc, char *argv[]) { int n; int fd[2]; pid_t pid; char *pager, *argv0; char line[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 */ else argv0 = pager; /* no slash in pager */ if (execl(pager, argv0, (char *)0) < 0) err_sys("execl error for %s", pager); } exit(0); }
popen和pclose函数 fig15.11
#include "apue.h" #include <sys/wait.h> #define PAGER "${PAGER:-more}" /* environment variable, or default */ int main(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); }