程式A標準輸出重定向B的標準輸入（c++）
阿新 • • 發佈：2018-12-04
背景：兩個程式A,B，B有自己的操作.現將A的標準輸出和B的標準輸入重定向，B的標準輸入和A的標準輸出重定向到一起。使得A收到輸入等同B收到輸入，邏輯處理後A可以直接使用結果。
B必須是一個可執行檔案。起初研究了一下popen，但這個函式只能實現單向流動，要麼w,要麼r。後來又研究了一下pipe管道，但管道基本是半雙工的，要實現A B互通，只能是兩個pipe來實現，管道的一端關閉寫，一端關閉讀。
相關技術(簡單解釋)：
協同程序：程序自己提供輸入，子程序處理操作，程序最終獲取結果
streams管道：和一般的pipe不同的是，它是一個全雙工管道，其內部結構如圖
fork: 執行此函式會啟動兩個程序，會返回兩次，父程序返回子程序ID，子程序返回 0
dup:建立一個檔案描述符的副本
B程式一端，實現將收到的輸入字串進行反轉，寫到輸出
#include "sgapue.h" #include <string.h> #include "my_err.h" char *strrev(char *str) { char *p1, *p2; if (! str || ! *str) return str; for (p1 = str, p2 = str + strlen(str) - 1; p2 > p1; ++p1, --p2) { *p1 ^= *p2; *p2 ^= *p1; *p1 ^= *p2; } return str; } int main(void) { int n; char line[MAXLINE]; while ((n = read(STDIN_FILENO, line, MAXLINE)) > 0){ line[n] = 0; strrev(line); n = strlen(line); if (write(STDOUT_FILENO, line, n) != n){ err_sys("write err!!!"); } } exit(0); }
兩個自定義的標頭檔案如下，my_err.h 和 sgapue.h其實就是參考的Unix高階程式設計：
#include <errno.h> #include <stdarg.h> static void err_doit(int, int, const char *, va_list); /* * Nonfatal error related to a system call. * Print a message and return. */ void err_ret(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, errno, fmt, ap); va_end(ap); } /* * Fatal error related to a system call. * Print a message and terminate. */ void err_sys(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, errno, fmt, ap); va_end(ap); exit(1); } /* * Fatal error unrelated to a system call. * Error code passed as explict parameter. * Print a message and terminate. */ void err_exit(int error, const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, error, fmt, ap); va_end(ap); exit(1); } /* * Fatal error related to a system call. * Print a message, dump core, and terminate. */ void err_dump(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, errno, fmt, ap); va_end(ap); abort(); /* dump core and terminate */ exit(1); /* shouldn't get here */ } /* * Nonfatal error unrelated to a system call. * Print a message and return. */ void err_msg(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(0, 0, fmt, ap); va_end(ap); } /* * Fatal error unrelated to a system call. * Print a message and terminate. */ void err_quit(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(0, 0, fmt, ap); va_end(ap); exit(1); } /* * Print a message and return to caller. * Caller specifies "errnoflag". */ static void err_doit(int errnoflag, int error, const char *fmt, va_list ap) { char buf[MAXLINE]; vsnprintf(buf, MAXLINE, fmt, ap); if (errnoflag) snprintf(buf+strlen(buf), MAXLINE-strlen(buf), ": %s", strerror(error)); strcat(buf, "\n"); fflush(stdout); /* in case stdout and stderr are the same */ fputs(buf, stderr); fflush(NULL); /* flushes all stdio output streams */ }
#ifndef _APUE_H
#define _APUE_H
#define _XOPEN_SOURCE 600 /* Single UNIX Specification, Version 3 */
#include <sys/types.h> /* some systems still require this */
#include <sys/stat.h>
#include <sys/termios.h> /* for winsize */
#ifndef TIOCGWINSZ
#include <sys/ioctl.h>
#endif
#include <stdio.h> /* for convenience */
#include <stdlib.h> /* for convenience */
#include <stddef.h> /* for offsetof */
#include <string.h> /* for convenience */
#include <unistd.h> /* for convenience */
#include <signal.h> /* for SIG_ERR */
#define MAXLINE 4096 /* max line length */
/*
* Default file access permissions for new files.
*/
#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
/*
* Default permissions for new directories.
*/
#define DIR_MODE (FILE_MODE | S_IXUSR | S_IXGRP | S_IXOTH)
typedef void Sigfunc(int); /* for signal handlers */
#if defined(SIG_IGN) && !defined(SIG_ERR)
#define SIG_ERR ((Sigfunc *)-1)
#endif
#define min(a, b) ((a) < (b) ? (a) : (b))
#define max(a, b) ((a) > (b) ? (a) : (b))
/*
* Prototypes for our own functions.
*/
char *path_alloc(int *); /* Figure 2.15 */
long open_max(void); /* Figure 2.16 */
void clr_fl(int, int); /* Figure 3.11 */
void set_fl(int, int); /* Figure 3.11 */
void pr_exit(int); /* Figure 8.5 */
void pr_mask(const char *); /* Figure 10.14 */
Sigfunc *signal_intr(int, Sigfunc *); /* Figure 10.19 */
int tty_cbreak(int); /* Figure 18.20 */
int tty_raw(int); /* Figure 18.20 */
int tty_reset(int); /* Figure 18.20 */
void tty_atexit(void); /* Figure 18.20 */
#ifdef ECHO /* only if <termios.h> has been included */
struct termios *tty_termios(void); /* Figure 18.20 */
#endif
void sleep_us(unsigned int); /* Exercise 14.6 */
ssize_t readn(int, void *, size_t); /* Figure 14.29 */
ssize_t writen(int, const void *, size_t); /* Figure 14.29 */
void daemonize(const char *); /* Figure 13.1 */
int s_pipe(int *); /* Figures 17.6 and 17.13 */
int recv_fd(int, ssize_t (*func)(int,
const void *, size_t));/* Figures 17.21 and 17.23 */
int send_fd(int, int); /* Figures 17.20 and 17.22 */
int send_err(int, int,
const char *); /* Figure 17.19 */
int serv_listen(const char *); /* Figures 17.10 and 17.15 */
int serv_accept(int, uid_t *); /* Figures 17.11 and 17.16 */
int cli_conn(const char *); /* Figures 17.12 and 17.17 */
int buf_args(char *, int (*func)(int,
char **)); /* Figure 17.32 */
int ptym_open(char *, int); /* Figures 19.8, 19.9, and 19.10 */
int ptys_open(char *); /* Figures 19.8, 19.9, and 19.10 */
#ifdef TIOCGWINSZ
pid_t pty_fork(int *, char *, int, const struct termios *,
const struct winsize *); /* Figure 19.11 */
#endif
int lock_reg(int, int, int, off_t, int, off_t); /* Figure 14.5 */
#define read_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLK, F_RDLCK, (offset), (whence), (len))
#define readw_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLKW, F_RDLCK, (offset), (whence), (len))
#define write_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLK, F_WRLCK, (offset), (whence), (len))
#define writew_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLKW, F_WRLCK, (offset), (whence), (len))
#define un_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLK, F_UNLCK, (offset), (whence), (len))
pid_t lock_test(int, int, off_t, int, off_t); /* Figure 14.6 */
#define is_read_lockable(fd, offset, whence, len) \
(lock_test((fd), F_RDLCK, (offset), (whence), (len)) == 0)
#define is_write_lockable(fd, offset, whence, len) \
(lock_test((fd), F_WRLCK, (offset), (whence), (len)) == 0)
void err_dump(const char *, ...); /* Appendix B */
void err_msg(const char *, ...);
void err_quit(const char *, ...);
void err_exit(int, const char *, ...);
void err_ret(const char *, ...);
void err_sys(const char *, ...);
void log_msg(const char *, ...); /* Appendix B */
void log_open(const char *, int, int);
void log_quit(const char *, ...);
void log_ret(const char *, ...);
void log_sys(const char *, ...);
void TELL_WAIT(void); /* parent/child from Section 8.9 */
void TELL_PARENT(pid_t);
void TELL_CHILD(pid_t);
void WAIT_PARENT(void);
void WAIT_CHILD(void);
#endifA端的程式：先建立兩個streams管道 fd0, fd1.呼叫fork，根據其兩次返回進行邏輯分支，子程序就進行dup繫結標準輸入輸出，執行execel啟動B；父程序直接將stdin輸入寫到stdout.
#include "sgapue.h"
#include "my_err.h"
#include <iostream>
#include <sys/socket.h>
using namespace std;
static void sig_pipe(int);
int main(void) {
int n;
int fd[2];
pid_t pid;
char line[MAXLINE];
if (signal(SIGPIPE, sig_pipe) == SIG_ERR)
err_sys("signal error");
if (s_pipe(fd) < 0)
err_sys("pip_err");
if ((pid = fork()) < 0) {
err_sys("fork err");
} else if (pid > 0) {//parent
close(fd[1]);
while (fgets(line, MAXLINE, stdin) != NULL) {
n = strlen(line);
if (write(fd[0], line, n) != n)
err_sys("write err to pipe");
if ((n = read(fd[0], line, MAXLINE)) < 0)
err_sys("read err from pipe");
if (n == 0) {
err_msg("child close pipe");
break;
}
line[n] = 0;
if (fputs(line, stdout) == EOF)
err_sys("fputs err");
}
} else {//child
close(fd[0]);
if (fd[1] != STDIN_FILENO && dup2(fd[1], STDIN_FILENO) != STDIN_FILENO)
err_sys("dup2 err to stdin");
if (fd[1] != STDOUT_FILENO && dup2(fd[1], STDOUT_FILENO) != STDOUT_FILENO)
err_sys("dup2 err to stdout");
if (execl("./cortest", "cortest", (char *) 0) < 0)
err_sys("execl err");
}
exit(0);
}
static void sig_pipe(int signo) {
cout << "SIGPIPE caught" << endl;
exit(1);
}
int s_pipe(int fd[2]) {
return (socketpair(AF_UNIX, SOCK_STREAM, 0, fd));
}參考文獻
https://linux.die.net/man/2/dup2
https://www.jianshu.com/p/4a5f71b9bf1d
《unix環境高階程式設計》figure.17