分叉和管道C++奇怪輸出

Question

我要寫一個需要2個命令及其參數（最多5個）的任務，它會將一個輸出傳遞給另一個。然後它會循環，再次詢問兩個命令，直到輸入quit。

我遇到的問題是，在第二個循環中輸入值後，發生奇怪的事情，例如在輸入第二個命令（都出現在同一行）後立即輸出「Enter Command 1」。我還注意到，輸入ls -l然後cat例如，但輸入ls -l然後wc會導致問題。有人會介意看看，並可能幫助我嗎？我一整天都在努力工作，我還有一個多小時就完成了。

方面注意：是的，我意識到執行命令設置有點愚蠢，但我沒時間了，沒有時間擺弄它。有用。

#include <iostream> 
#include <string> 
#include <stdlib.h> 
#include <stdio.h> 
#include <unistd.h> 
#include <sys/wait.h> 
#include <sstream> 
using namespace std; 

int main(){ 
//Our imput strings that the user enters. 
string input1; 
string input2; 

//Temporary string. 
string s; 

//Array to hold the items passed in. 
string arg1[6]; 
string arg2[6]; 

//A count of how many items they passed in. 
int carg1; 
int carg2; 

//Loop until quit. 
while(true){ 
    //Set all our values to empty/zero 
    carg1 = 0; 
    carg2 = 0; 
    input1.clear(); 
    input2.clear(); 

    //Prompt for first command. 
    while(input1.empty()){ 
     cout << "Command One (or quit): "; 
     getline(cin, input1); 
    } 

    //Split the string by the space to get the pieces of the command. 
    istringstream iss1(input1); 
    while (getline(iss1, s, ' ')) { 
     arg1[carg1] = s; 
     carg1++; 
    } 

    //Check if command is quit and exit if true. 
    if(arg1[0].compare("quit") == 0){ 
     return 0; 
    } 

    //Prompt for command 2. 
    while(input2.empty()){ 
     cout << "Command Two: "; 
     cin >> input2; 
    } 

    //Once again, split based on spaces. 
    istringstream iss2(input2); 
    while (getline(iss2, s, ' ')) { 
     //arg2.push_front(s); 
     arg2[carg2] = s; 
     carg2++; 
    } 

    //Initialize the pipe. 
    int pipefd[2]; 
    if(pipe(pipefd) == -1){ 
     perror("Pipe"); 
     exit(EXIT_FAILURE); 
    } 

    //Create the fork to two processes. 
    int pid = fork(); 

    //Switch to check for parent and child. 
    switch(pid){ 
     case 0: //Child process 
      //Close the read pipe and standard input. 
      close(pipefd[0]); 
      close(1); 

      //Copy data 
      dup(pipefd[1]); 

      //Close other end of the pipe 
      close(pipefd[1]); 

      //Execute the first command. Based on how many params, call different ones. 
      switch(carg1){ 
       case 1: 
        execlp(arg1[0].c_str(), arg1[0].c_str(), (char*)NULL); 
        break; 
       case 2: 
        execlp(arg1[0].c_str(), arg1[0].c_str(), arg1[1].c_str(), (char*)NULL); 
        break; 
       case 3: 
        execlp(arg1[0].c_str(), arg1[0].c_str(), arg1[1].c_str(), arg1[2].c_str(), (char*)NULL); 
        break; 
       case 4: 
        execlp(arg1[0].c_str(), arg1[0].c_str(), arg1[1].c_str(), arg1[2].c_str(), arg1[3].c_str(), (char*)NULL); 
        break; 
       case 5: 
        execlp(arg1[0].c_str(), arg1[0].c_str(), arg1[1].c_str(), arg1[2].c_str(), arg1[3].c_str(), arg1[4].c_str(), (char*)NULL); 
        break; 
       case 6: 
        execlp(arg1[0].c_str(), arg1[0].c_str(), arg1[1].c_str(), arg1[2].c_str(), arg1[3].c_str(), arg1[4].c_str(), arg1[5].c_str(), (char*)NULL); 
        break; 
       case 7: 
        execlp(arg1[0].c_str(), arg1[0].c_str(), arg1[1].c_str(), arg1[2].c_str(), arg1[3].c_str(), arg1[4].c_str(), arg1[5].c_str(), arg1[6].c_str(), (char*)NULL); 
        break; 
      } 
      return 0; 
     case -1: //Error 
      perror("fork"); 
      exit(EXIT_FAILURE); 
     default: //Parent Process 
      //Wait for initial command to execute. 
      wait(&pid); 

      //Fork into two processes. 
      int pid2 = fork(); 

      //Switch based on child and parent. 
      switch(pid2){ 
       case 0: //Child process 
        //Close write end of pipe and standard output. 
        close(pipefd[1]); 
        close(0); 

        //Duplicate to standard input 
        dup(pipefd[0]); 

        //Close read end. 
        close(pipefd[0]); 

        //Execute proper command based on params 
        switch(carg2){ 
         case 1: 
          execlp(arg2[0].c_str(), arg2[0].c_str(), (char*)NULL); 
          break; 
         case 2: 
          execlp(arg2[0].c_str(), arg2[0].c_str(), arg2[1].c_str(), (char*)NULL); 
          break; 
         case 3: 
          execlp(arg2[0].c_str(), arg2[0].c_str(), arg2[1].c_str(), arg2[2].c_str(), (char*)NULL); 
          break; 
         case 4: 
          execlp(arg2[0].c_str(), arg2[0].c_str(), arg2[1].c_str(), arg2[2].c_str(), arg2[3].c_str(), (char*)NULL); 
          break; 
         case 5: 
          execlp(arg2[0].c_str(), arg2[0].c_str(), arg2[1].c_str(), arg2[2].c_str(), arg2[3].c_str(), arg2[4].c_str(), (char*)NULL); 
          break; 
         case 6: 
          execlp(arg2[0].c_str(), arg2[0].c_str(), arg2[1].c_str(), arg2[2].c_str(), arg2[3].c_str(), arg2[4].c_str(), arg2[5].c_str(), (char*)NULL); 
          break; 
         case 7: 
          execlp(arg2[0].c_str(), arg2[0].c_str(), arg2[1].c_str(), arg2[2].c_str(), arg2[3].c_str(), arg2[4].c_str(), arg2[5].c_str(), arg2[6].c_str(), (char*)NULL); 
          break; 
        } 
        return 0; 
       case -1: //Error 
        perror("fork"); 
        exit(EXIT_FAILURE); 
       default: //Parent Process 
        //wait(&pid2); 
        break; 
      } 
    } 
} 
} 

示例輸出：

nick@nick-VirtualBox ~/Documents/Assign10 $ ./z1615629 
Command One (or quit): ls -l 
Command Two: wc 
Command One (or quit): Command One (or quit): quit 

示例輸出：

nick@nick-VirtualBox ~/Documents/Assign10 $ ./z1615629 
Command One (or quit): ls -l 
Command Two: cat 
Command One (or quit): Command One (or quit): 
total 32 
-rwxr-xr-x 1 nick nick 13358 Nov 20 15:46 z1615629 
-rw-r--r-- 1 nick nick 4544 Nov 20 15:46 z1615629.cxx 
-rw-r--r-- 1 nick nick 8104 Nov 20 15:46 z1615629.o 

Answer 1

因爲你不使用的功能，你必須在你的命令不對稱行爲提示和閱讀循環：

//Prompt for first command. 
while (input1.empty()){ 
    cout << "Command One (or quit): "; 
    getline(cin, input1); 
} 

... 

//Prompt for command 2. 
while (input2.empty()){ 
    cout << "Command Two: "; 
    cin >> input2; 
} 

第二個命令只包含一個單詞。換行符被留下，​​在下一個循環中提供雙重提示。在第二個提示循環中使用getline(cin, input2)。如果你使用功能，你會得到一致性 - 功能使生活更輕鬆，而不是更難。

您需要關閉父進程中的管道。您還需要在wait()：

  default: //Parent Process 
       //wait(&pid2); 
       break; 

使用：

  default: // Parent process 
       close(pipefd[0]); 
       close(pipefd[1]); 
       while (wait(0) != -1) 
        ; 
       break; 

Answer 2

我知道這並沒有解決這個問題，但這裏的原代碼C++ - 指明分數。

我已經注意保持C++ 03兼容。我只假設TR1爲綁定（all_memory_fun_ref的咒語應該很容易寫）。

注意尺寸的減小：刪除88 LOC（> 50％）

#include <iostream> 
#include <string> 
#include <stdio.h> 
#include <unistd.h> 
#include <sys/wait.h> 
#include <sstream> 
#include <vector> 
#include <algorithm> 
#include <iterator> 
#include <tr1/functional> 
using namespace std; 

void execute(std::vector<string> const& arg1) { 
    vector<char const*> argv(arg1.size()); 
    transform(arg1.begin(), arg1.end(), argv.begin(), tr1::bind(&std::string::c_str, tr1::placeholders::_1)); 
    argv.push_back(NULL); 
    execvp(argv[0], (char* const*) &argv[0]); // TODO FIXME error handling? 
    exit(EXIT_FAILURE); 
} 

std::vector<string> getinput(std::string prompt) { 
    vector<string> result; 
    string input; 
    //Prompt for first command. 
    while(input.empty()) { 
     cout << prompt; 
     getline(cin, input); 
    } 
    //Split the string by the space to get the pieces of the command. 
    { 
     istringstream iss(input); 
     copy(istream_iterator<string>(iss), istream_iterator<string>(), back_inserter(result)); 
    } 
    return result; 
} 

int main() { 
    //Loop until quit. 
    while(true) { 
     const std::vector<string> cmd1 = getinput("Command One (or quit): "); 
     if(cmd1.empty() || cmd1[0] == "quit") { 
      return 0; 
     } 
     const std::vector<string> cmd2 = getinput("Command Two: "); 

     //Initialize the pipe. 
     int pipefd[2]; 
     if(pipe(pipefd) == -1) { 
      perror("Pipe"); 
      exit(EXIT_FAILURE); 
     } 
     int pid = fork();    //Create the fork to two processes. 
     switch(pid) {     // Switch to check for parent and child. 
      case 0:      // Child process 
       close(pipefd[0]);  // Close the read pipe and standard input. 
       close(1); 
       dup(pipefd[1]);   // Copy data 
       close(pipefd[1]);  // Close other end of the pipe 
       execute(cmd1); 
       return 0; 
      case -1:     // Error 
       perror("fork"); 
       exit(EXIT_FAILURE); 
      default:     // Parent Process 
       wait(&pid);    // Wait for initial command to execute. 
       int pid2 = fork();  // Fork into two processes. 
       switch(pid2) {   // Switch based on child and parent. 
       case 0:     // Child process 
        close(pipefd[1]); // Close write end of pipe and standard output. 
        close(0); 
        dup(pipefd[0]);  // Duplicate to standard input 
        close(pipefd[0]); // Close read end. 
        execute(cmd2);  // Execute proper command based on params 
        return 0; 
       case -1:    // Error 
        perror("fork"); 
        exit(EXIT_FAILURE); 
       default:    // Parent Process 
        //wait(&pid2); 
        break; 
       } 
     } 
    } 
} 

免責聲明它編譯，我還沒有運行它（我不知道什麼樣的輸入給它餵食，以及如何操作。）