Myshell分段错误，获取输入可能存在问题？

Question

我一直在这个项目上工作了一段时间。目的是制作一个可以完成所有shell命令（除cd之外）的正常运行的shell。它几乎做了我希望它做的所有事情，除了一些事情。首先，当我将'&'表示后台处理时，它会执行此操作，但不会打印另一个myshell>行。我仍然可以输入内容，但是myshell>永远不会显示，无论我在哪里放置另一个cout < <“myshell>”;。

另一个问题是，如果我按下回车键，使得myString为空，很多次，它会以seg故障使程序崩溃。另外，在我执行'&'后台处理并按回车让myshell>恢复后，它会打印一个myshell>，然后在下一次输入中选择seg错误。如果我没有解释清楚，我很抱歉，但这真的让我发疯。如果您有任何建议，请告诉我。

#include <stdio.h> 
#include <iostream> 
#include <unistd.h> 
#include <cstdlib> 
#include <cstring> 
#include <sys/types.h> 
#include <cstdio> 
#include <sys/wait.h> 
#include <stdio.h> 

/*Function that parses the command the user inputs. 
    It takes myArgv and myString as inputs. 
    It returns the value of exitcond, which is used to see if the user wants to exit or not. 
    Also, this is where myString is tokenized using strok()*/ 
int parseCommand(char *myArgv[10], char myString[255]) 
{ 
    int exitcond=0; 
    if((strcmp(myArgv[0], "exit") == 0)||(strcmp(myArgv[0], "quit")==0)) 
    { 
     exitcond = 1; 
     return exitcond; 
    } 
    int i; 
    char *token; 
    token = strtok(myString," "); 
     i=0; 
     while (token != NULL) 
     { 
      myArgv[i] = token; 
      token = strtok(NULL," "); 
      i++; 
     } 

     /* 
     * Set the last entry our new argv to a null char 
     * (see man execvp to understand why). 
     */ 
     myArgv[i] = '\0'; 
    return exitcond; 
} 
/*Function that gets the command from the user and sees if they want 
background processing or not (presence of '&'). 
    It takes inputs of choose and myString. choose is the variable for 
whether background processing is necessary or not, while myString is 
an empty character array. 
    It outputs the value of the choose variable for lter use.*/ 
int getCommand(int choose, char myString[255]) 
{ 
    int i; 
    choose=0; 
    fgets(myString, 256, stdin); 
    if (myString[0]=='\0') 
    { 
     choose=0; 
     return choose; 
    } 
     for (i=0; myString[i]; i++) 
     { 
      if (myString[i]== '&') 
      { 
      choose=1; 
      myString[i]=' '; 
     } 

     if (myString[i] == '\n') 
     { 
      myString[i] = '\0'; 
     } 
    } 
    return choose; 
} 
/*Main function where all the calling of other functions and processes 
is done. This is where the user enters and exits the shell also. All 
usage of fork, pid, waitpid and execvp is done here.*/ 
int main() 
{ 
    using namespace std; 
    int exitCondition=0, i=0, status; 
    char myString[255]; 
    char *token, *myArgv[10]; 
    pid_t pid, waiting; 
    int bg=0; 
    while (!exitCondition) 
    { 
     /* print a prompt and allow the user to enter a stream of characters */ 
     cout << "myshell> "; 
     bg=0; 
     int choose=0; 
     bg=getCommand(choose,myString); 
     exitCondition=parseCommand(myArgv,myString); 
     if(exitCondition==1) 
     { 
      cout<<"Thank you for using my shell.\n"; 
     } 

    else { 
    /* while (myString[0]=='\0') 
     { 
      cout<<"myshell> "; 
      bg=getCommand(choose,myString); 
     }*/ 
     /* The user has a command, so spawn it in a child process */ 

     pid = fork(); 

     if (pid == -1) 
     { 
      /* to understand why this is here, see man 2 fork */ 
      cout << "A problem arose, the shell failed to spawn a child process" << endl; 
      return(1); 
     } 

     else if (pid == 0) 
     { 
      // Child process 
      execvp(myArgv[0],myArgv); 
      cout << "Bad command or file name, please try again!\n" << endl; 
      return 0; 
     } else { 
      /* This makes sure that the spawned process is run in the foreground, 
       because the user did not choose background */ 
      if(bg==0) 
      { 
       waitpid(pid,NULL,0); 

      } 
      } 

    } 
} 
return 0; 
} 

Answer 1

好的，你有三个错误，其中一个导致段错误。在其他人中，人们会将数组中的垃圾参数传递给execvp，另一个会泄漏后台作业的僵尸进程。

我已经与其中的错误都与修复以及修正代码并注明其[请原谅无偿风格清理]：

#include <cstdio> 
#include <iostream> 
#include <sys/types.h> 
#include <sys/wait.h> 
#include <stdio.h> 
#include <string.h> 
#include <unistd.h> 

#define AVCOUNT  100 
#define STRBUFLEN 2000 

/*Function that parses the command the user inputs. 
    It takes myArgv and myString as inputs. 
    It returns the value of exitcond, which is used to see if the user wants to 
    exit or not. 
    Also, this is where myString is tokenized using strok()*/ 
int 
parseCommand(char **myArgv, char *myString) 
{ 
    char *token; 
    char *bp; 
    int exitcond = 0; 
    int i; 

    // NOTE/BUG: original check for exit/quit was here -- at this point 
    // myArgv is undefined (hence the segfault) 

    // NOTE/BUG: your original loop -- at the end i was one beyond where it 
    // should have been so that when myArgv gets passed to execvp it would 
    // have an undefined value at the end 
#if 0 
    token = strtok(myString, " "); 
    i = 0; 
    while (token != NULL) { 
     myArgv[i] = token; 
     token = strtok(NULL, " "); 
     i++; 
    } 
#endif 

    // NOTE/BUGFIX: here is the corrected loop 
    i = 0; 
    bp = myString; 
    while (1) { 
     token = strtok(bp, " "); 
     bp = NULL; 

     if (token == NULL) 
      break; 

     myArgv[i++] = token; 
    } 

    /* 
    * Set the last entry our new argv to a null pointer 
    * (see man execvp to understand why). 
    */ 
    // NOTE/BUG: with your code, i was one too high here 
    myArgv[i] = NULL; 

    // NOTE/BUGFIX: moved exit/quit check to here now that myArgv is valid 
    token = myArgv[0]; 
    if (token != NULL) { 
     if ((strcmp(token, "exit") == 0) || (strcmp(token, "quit") == 0)) 
      exitcond = 1; 
    } 

    return exitcond; 
} 

/*Function that gets the command from the user and sees if they want 
    background processing or not (presence of '&'). 
    It takes inputs of choose and myString. choose is the variable for 
    whether background processing is necessary or not, while myString is 
    an empty character array. 
    It outputs the value of the choose variable for lter use.*/ 
int 
getCommand(int choose, char *myString) 
{ 
    int i; 

    choose = 0; 
    fgets(myString, STRBUFLEN, stdin); 

    if (myString[0] == '\0') { 
     choose = 0; 
     return choose; 
    } 

    for (i = 0; myString[i]; i++) { 
     if (myString[i] == '&') { 
      choose = 1; 
      myString[i] = ' '; 
     } 

     if (myString[i] == '\n') { 
      myString[i] = '\0'; 
      break; 
     } 
    } 

    return choose; 
} 

/*Main function where all the calling of other functions and processes 
    is done. This is where the user enters and exits the shell also. All 
    usage of fork, pid, waitpid and execvp is done here.*/ 
int 
main() 
{ 
    using namespace std; 
    int exitCondition = 0; 
    int status; 
    char myString[STRBUFLEN]; 
    char *myArgv[AVCOUNT]; 
    pid_t pid; 
    int bg = 0; 

    while (!exitCondition) { 
     // NOTE/BUGFIX: without this, any background process that completed 
     // would become a zombie because it was never waited for [again] 
     // reap any finished background jobs 
     while (1) { 
      pid = waitpid(0,&status,WNOHANG); 
      if (pid < 0) 
       break; 
     } 

     /* print a prompt and allow the user to enter a stream of characters */ 
     cout << "myshell> "; 
     bg = 0; 
     int choose = 0; 

     bg = getCommand(choose, myString); 

     exitCondition = parseCommand(myArgv, myString); 
     if (exitCondition == 1) { 
      cout << "Thank you for using my shell.\n"; 
      break; 
     } 

     /* while (myString[0]=='\0') { cout<<"myshell> "; bg=getCommand(choose,myString); } */ 
     /* The user has a command, so spawn it in a child process */ 

     pid = fork(); 

     if (pid == -1) { 
      /* to understand why this is here, see man 2 fork */ 
      cout << "A problem arose, the shell failed to spawn a child process" << endl; 
      return 1; 
     } 

     if (pid == 0) { 
      // Child process 
      execvp(myArgv[0], myArgv); 
      cout << "Bad command or file name, please try again!\n" << endl; 
      return 1; 
     } 

     /* This makes sure that the spawned process is run in the 
     foreground, because the user did not choose background */ 
     if (bg == 0) 
      waitpid(pid, &status, 0); 
    } 

    return 0; 
}