如何在两个程序之间共享内存中存储和访问数据？

Question

我有一个家庭作业要写两个程序，一个生产者和一个消费者。生产者必须将一个正整数作为用户的输入，预先对其进行计算(在本例中是Collatz猜想)，并将结果存储在共享内存中。使用者程序必须访问此结果并打印它。

问题是，我已经能够创建、存储和打印字符数组(使用mmap和memcpy)，但我似乎不能对整数或整数数组做同样的操作，这是我在计算中将生成的数据类型。我也尝试将计算存储为字符数组，但无法将ints转换为字符。

目前，生产者程序只是将结果打印到控制台，而不是存储结果。

生产者

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/mman.h>

int main()
{
    /* The size (in bytes) of shared-memory object */
    const int SIZE = 4096;

    /* The name of shared-memory object */
    const char* Obj = "Shm";

    /* The shared-memory file descriptor */
    int shm_fd;

    /* The pointer to shared-memory object */
    void* ptr;

    /* Create the shared-memory object */
    shm_fd = shm_open(Obj, O_CREAT | O_RDWR, 0666);

    /* Configure the size of the shared-memory object */
    ftruncate(shm_fd, SIZE);

    /* Map the shared-memory object in the address space of the process */
    ptr = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);

    if (ptr == MAP_FAILED)
    {
        printf("Map failed\n");
        return -1;
    }


    //** NEW CODE //

    // calculate based on user input 
    int userInput; // variable to store user int input

    printf("please input a starting number for the collatz conjecture: \n");
    if (scanf("%d", &userInput) == 1) {
        // print each number in the conjecture 
        printf("%d", userInput);
        
        
        // TEST AREA 
    
        int input2 = 5; // THIS WORKS TO SAVE A STRING, BUT NOT INTS
        
        //char inputAr[SIZE];

        //char temp[] = (char)input2;
        //strcat(inputAr, temp);
        
        memcpy(ptr, &input2, SIZE);

        //  TEST AREA

        //char input[SIZE];
        //char temp[10];
        //strcpy(temp, "40123456");
        ////char temp[] = "4";
        //strcat(input, temp);
        //strcpy(temp, " 6");
        //strcat(input, temp);
        //memcpy(ptr, &input, SIZE);




        printf(" ");
        while (userInput != 1) {
            if (userInput % 2 == 0) {
                userInput = userInput / 2;
                printf("%d", userInput);
                printf(" ");
            }
            else {
                userInput = userInput * 3 + 1;
                printf("%d", userInput);
                printf(" ");
            }
        }// end while

    }

    //** END NEW CODE

    /* Create a message and write it to the shared-memory object */
    //printf("Please input a character string: \n");
    //fgets(ptr, SIZE, stdin);
    printf("Writing the message to the shared memory is done! \n");

    return 0;
}

消费者

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/mman.h>

int main()
{

    /* The size (in bytes) of shared-memory object */
    const int SIZE = 4096;

    /* The name of shared-memory object */
    const char* Obj = "Shm";

    /* The shared-memory file descriptor */
    int shm_fd;

    /* The pointer to shared-memory object */
    void* ptr;

    /* Open the shared-memory object */
    shm_fd = shm_open(Obj, O_RDONLY, 0666);

    if (shm_fd == -1)
    {
        printf("Shared memory failed\n");
        exit(-1);
    }

    /* Map the shared-memory object in the address space of the process */
    ptr = mmap(0, SIZE, PROT_READ, MAP_SHARED, shm_fd, 0);

    if (ptr == MAP_FAILED)
    {
        printf("Map failed\n");
        exit(-1);
    }

    
    /* Read from the shared-memory object */
    //printf("Test message: %d", (int*)ptr);
    printf("\n");
    printf("The message read from the shared memory: %s", (char*)ptr);
    

    /* Remove the shared-memory object */
    if (shm_unlink(Obj) == -1)
    {
        printf("Error removing %s\n", Obj);
        exit(-1);
    }

    return 0;
}

Answer 1

单整数

请记住，在生产者程序中，您已经将整数input2存储在共享内存中，因此需要将其打印为整数，而不是字符数组。而不是

printf("The message read from the shared memory: %s", (char *)ptr);

你需要把它写成

int *integer_array = (int *) ptr;
printf("The message read from the shared memory: %d", *integer_array);

这会将ptr (即void *)类型转换为整数指针(int *)，您可以取消引用以获得input2的值。此外，"%d"用于整数，而不是"%s"。

整数阵

要打印出一个整数数组，而不仅仅是一个整数数组，就必须在ptr中为number_of_ints * sizeof(int)提供足够的空间。在每次Collatz猜想迭代中，只需将结果存储在数组中，如下所示：

int *integer_array = (int *) ptr;
while (userInput != 1) {
    if (userInput % 2 == 0) {
        userInput = userInput / 2;
    } else {
        userInput = userInput * 3 + 1;
    }

    *(integer_array++) = userInput;
}

一旦生产者程序完成，消费者程序可以打印出以下每一个数字：

int *integer_array = (int *) ptr;
for (int i = 0; i < number_of_ints; i++) {
    printf("%d ", integer_array[i]);
}