Question

编辑：现在我知道错误在主函数中如果我删除它：

*A=0;
*NH=0;
*NS=0;
*in_boat=0;

然后我运行它没有段错误，为什么会发生这种情况？

以下代码返回分段错误11..i我不知道原因：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <semaphore.h>
#include <sys/stat.h> 
#include <sys/shm.h>
#include <sys/wait.h>
#include <time.h>

//--------------------Function declarations
void hacker_pier(int x);
void serf_pier(int x);


//--------------------Global variables
sem_t *sem_var, *sem_entry_pier, *sem_start_row, *sem_board_h, *sem_board_s, *sem_row_finished, *sem_file;//Semaphores
int *A,*I,*NH,*NS,*in_boat;//Count variables
int H,S,R,P;//User input variables
FILE *fp;//File pointer


int main(int argc, char *argv[])
{

    int pid, pid2, pid3, pid4;//IDs for processes
    int id_sem_var, id_sem_entry_pier, id_sem_start_row, status, id_sem_board_h, id_sem_board_s, id_sem_row_finished, id_sem_file;//IDs for shared memory segment for semaphores    
    int id_I_hacker, id_I_serf, id_NH, id_NS, id_in_boat, id_A;//IDs for shared memory segment for counter variables
    int i,x,y;//Temp variables

    srand(time(NULL));//Seeding random function

    P = atoi(argv[1]);//retrieving values from command line 
    H = atoi(argv[2]);  
    S = atoi(argv[3]);  
    R = atoi(argv[4]);


    if((argc!=5)||(P==0 || P%2!=0)|| (H<0 || H>5000)|| (S<0 || S>5000)|| (R<0 || R>5000))//Checking validity of user input
    {
        fprintf(stderr,"Invalid value of argument\n");
        return 1;
    }

    H*=1000;//converting miliseconds to micro seconds, usleep() takes micro seconds as argument
    S*=1000;
    R*=1000;

    fp = fopen("rivercrossing.out","w");//Opening file

    if(fp==NULL)
    {
        fprintf(stderr,"Unable to access rivercrossing.out\n");     
        return 2;
    }




//--------------------Creating shared memory segment of semaphores
    id_sem_var = shmget(IPC_PRIVATE, sizeof(sem_t), (S_IRUSR|S_IWUSR));
    id_sem_entry_pier = shmget(IPC_PRIVATE, sizeof(sem_t), (S_IRUSR|S_IWUSR));
    id_sem_start_row = shmget(IPC_PRIVATE, sizeof(sem_t), (S_IRUSR|S_IWUSR));
    id_sem_board_h = shmget(IPC_PRIVATE, sizeof(sem_t), (S_IRUSR|S_IWUSR));
    id_sem_board_s = shmget(IPC_PRIVATE, sizeof(sem_t), (S_IRUSR|S_IWUSR));
    id_sem_file = shmget(IPC_PRIVATE, sizeof(sem_t), (S_IRUSR|S_IWUSR));
    id_sem_row_finished = shmget(IPC_PRIVATE, sizeof(sem_t), (S_IRUSR|S_IWUSR));

    sem_var = (sem_t *)shmat(id_sem_var, NULL, 0);  
    sem_entry_pier = (sem_t *)shmat(id_sem_entry_pier, NULL, 0);
    sem_start_row = (sem_t *)shmat(id_sem_start_row, NULL, 0);
    sem_board_h = (sem_t *)shmat(id_sem_board_h, NULL, 0);
    sem_board_s = (sem_t *)shmat(id_sem_board_s, NULL, 0);
    sem_row_finished = (sem_t *)shmat(id_sem_row_finished, NULL, 0);    
    sem_file = (sem_t *)shmat(id_sem_file, NULL, 0);


//--------------------Creating shared memory segment of counters
    id_A = shmget(IPC_PRIVATE, sizeof(int), 0777|IPC_CREAT);
    id_I_hacker = shmget(IPC_PRIVATE, sizeof(int), 0777|IPC_CREAT); 
    id_I_serf = shmget(IPC_PRIVATE, sizeof(int), 0777|IPC_CREAT);
    id_NH = shmget(IPC_PRIVATE, sizeof(int), 0777|IPC_CREAT);
    id_NS = shmget(IPC_PRIVATE, sizeof(int), 0777|IPC_CREAT);
    id_in_boat = shmget(IPC_PRIVATE, sizeof(int), 0777|IPC_CREAT);


    A = (int *) shmat(id_A, 0, 0);  
    NH = (int *) shmat(id_NH, 0, 0);    
    NS = (int *) shmat(id_NS, 0, 0);    
    in_boat = (int *) shmat(id_in_boat, 0, 0);

//--------------------Initializing semaphores
    sem_init(sem_var,1,1);
    sem_init(sem_entry_pier,1,1);
    sem_init(sem_start_row,1,0);
    sem_init(sem_row_finished,1,0);
    sem_init(sem_board_s,1,0);
    sem_init(sem_board_h,1,0);
    sem_init(sem_file,1,1);



    sem_wait(sem_var);
//--------------------Initializing counters
    *A=0;
    *NH=0;
    *NS=0;
    *in_boat=0; 


    return 0;
}

这实现了称为rivercrossing的同步问题。

我编译gcc rivercrossing.c -o rc并运行如下：./rc 2 2 2 200 其中第一个2是每个类别中生成的人数（serf，黑客），第二个和第三个2表示生成新进程黑客和serf的最大长度，最后200是最大长度巡航。

输出应该在文件中

Answer 1

您的一个或多个指针（A，NH，NS或in_boat）可能无效。这可能意味着shmat()返回了其错误指示值（根据手册页为(void *)-1）。您的代码应检查此错误指示值，并查看errno以找出shmat()失败的原因。

分段错误11我不知道为什么

1 个答案: