共享内存中的 C++ 二维数组（基于命令行参数）[关闭]

Question

我正在尝试将一个存在于共享内存段中的二维 (2D) 数组附加到 C 中的一个进程。编译时出现以下错误：

main.cpp:52:22: error: invalid conversion from ‘void*’ to ‘int (*)[2]’ [-fpermissive]
  shm_assemble = shmat(shmid_assemble,0,0);

编译命令为：

g++ main.cpp -o myworkshop

我的代码是这样的：

#include <iostream>
#include <cstring>
#include <ctime>
#include <cstdlib>
#include <cstdio>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <ctype.h>

#include "myheader.h"

void perror_exit(char *message);
bool init(int argc, char * argv[], int *Y);

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

    if(argc<3) {
        perror_exit("Usage: ./myworkshop -Y <value>\n");
        return(-1);
    }
    int i=0,n=0,child_pid=0,Y=0,shmid_paint=0,shmid_assemble=0,shmid_check=0,shmid_y=0,painter_empty=0,painter_full=0,checker_full=0,checker_empty=0,assembler_full=0,assembler_empty=0,ex=0;
    int *pids = new int[8];

    kill_message *shm_y;
    message *shm_paint,*shm_check;
    int (*shm_assemble)[2];

    if (!init(argc,argv,&Y)){
        std::cout << "Something is wrong with the arguments, try again\n";
        exit(-2);
    }

    if(Y==0) return 0; // if no products are to be created the program should exit

    const int SHMSIZE = sizeof(message);                // Shared Memory size = the size of a message
    const int assembler_SHMSIZE = sizeof(int[3*Y][2]);
    printf("assembler_SHMSIZE is: %d\n", assembler_SHMSIZE);
    const int kill_SHMSIZE = sizeof(kill_message);
    // srand(time(NULL));

    /* --- Shared memory creation --- */
    shmid_paint = shmget(IPC_PRIVATE, SHMSIZE, IPC_CREAT | 0666);
    shmid_assemble = shmget(IPC_PRIVATE, assembler_SHMSIZE, IPC_CREAT | 0666);
    shmid_check = shmget(IPC_PRIVATE, SHMSIZE, IPC_CREAT | 0666);
    shmid_y = shmget(IPC_PRIVATE, kill_SHMSIZE, IPC_CREAT | 0666);

    shm_paint = (message*)shmat(shmid_paint,NULL,0);
    shm_assemble = (int **)shmat(shmid_assemble,0,0);
    shm_check = (message*)shmat(shmid_check,NULL,0);
    shm_y = (kill_message*)shmat(shmid
}

我在这里做错了什么？

我阅读了此similar question，但我要么没有正确理解答案，要么静态大小对我的情况没有帮助。

我的目标是拥有一个由 [3*Y][2] 整数组成的二维数组，其中 Y 作为 main 中的参数给出，并在我未包括在此处的 init 函数中正确初始化。

Answer 1

好的，答案很简单。 我不得不将 shm_write_assembler 声明为 int **。我最初的 int (shm_write_assembler)[2] 在 C 中工作，就像在我用作示例但不在 C++ 中的相关问题中一样。改变这一点使我的代码像魅力一样工作。

以下是更正后的代码：

#include <iostream>
#include <cstring>
#include <ctime>
#include <cstdlib>
#include <cstdio>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <ctype.h>

#include "myheader.h"

void perror_exit(char *message);
bool init(int argc, char * argv[], int *Y);

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

    if(argc<3) {
        perror_exit("Usage: ./myworkshop -Y <value>\n");
        return(-1);
    }
    int i=0,n=0,child_pid=0,Y=0,shmid_paint=0,shmid_assemble=0,shmid_check=0,shmid_y=0,painter_empty=0,painter_full=0,checker_full=0,checker_empty=0,assembler_full=0,assembler_empty=0,ex=0;
    int *pids = new int[8];

    kill_message *shm_y;
    message *shm_paint,*shm_check;
    int **shm_assemble;

    if (!init(argc,argv,&Y)){
        std::cout << "Something is wrong with the arguments, try again\n";
        exit(-2);
    }

    if(Y==0) {
        delete[] pids;
        return 0; // if no products are to be created the program should exit
    }

    const int SHMSIZE = sizeof(message);                // Shared Memory size = the size of a message
    const int assembler_SHMSIZE = sizeof(int[3*Y][2]);
    printf("assembler_SHMSIZE is: %d\n", assembler_SHMSIZE);
    const int kill_SHMSIZE = sizeof(kill_message);
    // srand(time(NULL));

    /* --- Shared memory creation --- */
    shmid_paint = shmget(IPC_PRIVATE, SHMSIZE, IPC_CREAT | 0666);
    shmid_assemble = shmget(IPC_PRIVATE, assembler_SHMSIZE, IPC_CREAT | 0666);
    shmid_check = shmget(IPC_PRIVATE, SHMSIZE, IPC_CREAT | 0666);
    shmid_y = shmget(IPC_PRIVATE, kill_SHMSIZE, IPC_CREAT | 0666);

    shm_paint = (message*)shmat(shmid_paint,NULL,0);
    shm_assemble = (int**)shmat(shmid_assemble,NULL,0);
    shm_check = (message*)shmat(shmid_check,NULL,0);
    shm_y = (kill_message*)shmat(shmid_y,NULL,0);

    /* --- Semaphore creation --- */
    painter_empty = semget(IPC_PRIVATE,1,IPC_CREAT | 0666);
    painter_full = semget(IPC_PRIVATE,1,IPC_CREAT | 0666);

    checker_empty = semget(IPC_PRIVATE,1,IPC_CREAT | 0666);
    checker_full = semget(IPC_PRIVATE,1,IPC_CREAT | 0666);

    assembler_empty = semget(IPC_PRIVATE,1,IPC_CREAT | 0666);
    assembler_full = semget(IPC_PRIVATE,1,IPC_CREAT | 0666);

    delete[] pids;
}