c - 用 c 编写我自己的 shell - free() 导致问题

Question

我正在尝试编写自己的 shell，但有些东西无法与分配和空闲一起使用。我一遍又一遍地检查我的代码，我无法理解为什么我的自由函数给我带来了问题......当我不使用它时，一切正常，但是当我使用它时，代码在第二次迭代后停止工作。 ..我非常感谢您的帮助...

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <limits.h> //for PATH_MAX - longest path name permited in linux
#include <sys/wait.h>
#include <fcntl.h>

typedef struct{
char **parametersArray; //this array contains the command and the parameters
int size_of_array; //the number of strings in the array
int toFileFlag; //if we wnat to write to file
char *toFile; //name of file to write to
int fromFileFlag;//if we wnat to read from file
char *fromFile; //name of file to read to
}UserInput;

int runInBackground = 0; //is command running in background? if so, runInBackground=1;

//********************************************************************************************************************
//functions list:

UserInput* inputTokenization(char *a); //recieve string of the user input, and returns pointer to struct of UserInput.   
void execCommand(UserInput *user_input); //exec the requestd command with the parameters given 
void free_All_Allocations(UserInput *userinput); 

 //*******************************************************************************************************************
int main(int argc, char *argv[])
{
    char userInputTxt[LINE_MAX]; //the line the user enters (hopefully command+parameters)   
    UserInput *u_i;   
    int i = 0;

    while(1)
    {
        i = 0;
        printf("\033[1;35m"); //print in with color (purple)
        printf("### "); //### is the prompt I chose    
        fflush(stdout);
        memset(userInputTxt, 0, LINE_MAX); //cleaning array from previous iteration 
        read(0, userInputTxt, LINE_MAX); 

        if(strcmp(userInputTxt, "exit\n") == 0) //exit the program if the user enters "exit"       
            exit(EXIT_SUCCESS);

        u_i = inputTokenization(userInputTxt); //parsing the char array userInputTxt
        execCommand(u_i); 
        free_All_Allocations(u_i);
    }

}

UserInput* inputTokenization(char *a)
{   
    int i=0, size;    
    size = strlen(a);
    UserInput *user_input = (UserInput*)malloc(sizeof(UserInput)*1); 
    if(user_input == NULL)
     {
        perror("failed to allocate memory");
        exit(EXIT_FAILURE); 
    }


    user_input->fromFileFlag = 0;
    user_input->toFileFlag = 0;
    user_input->size_of_array = 2;

    //counting how many token we have
    while(i<size)
    {
        if(a[i] == ' ')
            (user_input->size_of_array)++;
        if (a[i] != '<' || a[i] != '>' )
            break;
        i++;
    }
    printf("%d\n", user_input->size_of_array);

    //we don't want to change original array(a), so we'll copy a to tmp and use tmp
    char *tmp = (char*)malloc(size+1);
    if(tmp == NULL)
     {
        perror("failed to allocate memory");
        exit(EXIT_FAILURE); 
    }
    strncpy(tmp, a, size-1);

    //we'll allocate array of arrays. It's size: number of tokens in the original array, even though we might not use all of it-
    //some tokens might be name of file to read or write to
    user_input->parametersArray = (char**)malloc(user_input->size_of_array);
    if(user_input->parametersArray == NULL)
     {
        perror("failed to allocate memory");
        exit(EXIT_FAILURE); 
    }

    i=0;    
    char* token = strtok(tmp, " ");   
    user_input->parametersArray[i] = (char*)malloc(strlen(token)+1);
    if(user_input->parametersArray[i] == NULL)
     {
        perror("failed to allocate memory");
        exit(EXIT_FAILURE); 
    }
    strcpy(user_input->parametersArray[i], token);
    i++; 

    while(token != NULL)
    {
        token = strtok(NULL, " ");
        if(token !=NULL)
        {
            if(strcmp(token, "<") != 0 && strcmp(token, ">") !=0 && strcmp(token, "&") != 0)
            {
                user_input->parametersArray[i] = (char*)malloc(strlen(token)+1);
                if(user_input->parametersArray[i] == NULL)
                {
                    perror("failed to allocate memory");
                    exit(EXIT_FAILURE); 
                }
                strcpy(user_input->parametersArray[i], token);                
                i++;
                continue;
            }

            if(strcmp(token, "<") == 0)
            {
               user_input->fromFileFlag = 1;
               token = strtok(NULL, " ");
               if(token !=NULL)
               {
                   user_input->fromFile = (char*)malloc(strlen(token)+1);
                   if(user_input->fromFile == NULL)
                    {
                        perror("failed to allocate memory");
                        exit(EXIT_FAILURE); 
                    }
                   strcpy(user_input->fromFile, token);
               }               
            }

            if(strcmp(token, ">") == 0)
            {
               user_input->toFileFlag = 1;
               token = strtok(NULL, " ");
               if(token != NULL)
               {
                   user_input->toFile = (char*)malloc(strlen(token)+1);
                   if(user_input->toFile == NULL)
                    {
                        perror("failed to allocate memory");
                        exit(EXIT_FAILURE); 
                    }
                   strcpy(user_input->toFile, token);
               }               
            }
            if(strcmp(token, "&") == 0)
            {
               runInBackground = 1;
               break;                            
            }

        }
    }        

    user_input->parametersArray[i] = NULL;

    free(tmp);
    return user_input;       
}

void execCommand(UserInput *user_input)
{
   pid_t pid;
   int status;   

    pid = fork();

    if(pid == -1) //fork failed
    {
        perror("fork() failed");
        exit(EXIT_FAILURE);
    }
    if(pid == 0) //child process
    {        
        if(user_input->fromFileFlag == 1) //if we have file to read from
        {
            close(0);
            if(open(user_input->fromFile, O_RDONLY) == -1) 
            {                
                perror("open file to read failed");
                exit(EXIT_FAILURE);
            }
        }
        if(user_input->toFileFlag == 1) //if we have file to write to
        {
            close(1);
            if(open(user_input->toFile, O_WRONLY | O_CREAT, 0766) == -1)
            {
                perror("open file to write failed");
                exit(EXIT_FAILURE);
            }
        }

        if(execvp(user_input->parametersArray[0], user_input->parametersArray) == -1)
        {
            perror("execvp() failed");
            exit(EXIT_FAILURE);
        }
    }

    if(runInBackground == 0) //as long as this is the only command to execute, 
        waitpid(pid, &status, 0); //wait until chile process (execvp) finish. Otherwise, father process go again, and chile process run in background   
}

void free_All_Allocations(UserInput *userinput)
{
    int i=0;

    while(userinput->parametersArray[i] != NULL)
     {                
         free(userinput->parametersArray[i]);
         i++;        
     }    

     free(userinput->parametersArray);   
     if(userinput->fromFileFlag == 1)
         free(userinput->fromFile);
     if(userinput->toFileFlag == 1)
        free(userinput->toFile);       
     free(userinput);    
}

Answer 1

我建议使用valgrind。

使用标志 -ggdb3 编译您的代码，然后使用您的程序执行 valgrind。它会显示程序执行期间所有无效的读取和写入。不仅如此，它还会准确地告诉您它们发生在哪一行以及相应的函数调用跟踪。

This question如果您是 valgrind 的初学者，这是一个很好的起点。