两个C程序之间的管道

Question

在过去的几个小时里，我一直在让管道在两个程序之间工作，我被卡住了，不确定我是否做错了什么。我的程序的思想是，我将使用interface.c打开一个管道，然后执行db.c。我想用两个管道在两个不同的程序之间进行通信。现在，interface.c是"父"，db.c是"子"，我不确定我是否通过execl命令正确地将参数传递给我的管道。一切都编译正确，但当我试图运行接口程序时，我得到一个错误:"错误的文件编号"。有没有可能我没有正确使用管道?目前，我只是想让我的程序发送一个整数，值，通过管道到db.c。如有任何帮助，不胜感激。

interface.c的代码

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <sys/wait.h>
//PIPES:
//
//Parent: reads from P1_READ, writes on P1_WRITE
//Child:  reads from P2_READ, writes on P2_WRITE
#define P1_READ     0
#define P2_WRITE    1
#define P2_READ     2
#define P1_WRITE    3
// the total number of pipe *pairs* we need
#define NUM_PIPES   2
int main(int argc, char *argv[])
{
    //Create Pipe Array
    int fd[2*NUM_PIPES];
    //For Parameter Passing:
    char param0[20];        //P1_Read
    char param1[20];        //P2_Write
    char param2[20];        //P2_Read
    char param3[20];        //P1_Write
    snprintf(param0, sizeof(param0), "%d" , fd[0]);
    snprintf(param1, sizeof(param1), "%d" , fd[1]);
    snprintf(param2, sizeof(param2), "%d" , fd[2]);
    snprintf(param3, sizeof(param3), "%d" , fd[3]);
    //Variables
    pid_t pid;
    int val = 42;
    //Allocate the PIPES
    for (int i=0; i<NUM_PIPES; ++i)
    {
        if(pipe(fd+(i*2)) < 0)
        {
            perror("Failed to allocate the pipes");
            exit(EXIT_FAILURE);
        }
    }
     //If the fork of the program does not work:
    if ((pid = fork()) < 0)
    {
        perror("Failed to fork process");
        return EXIT_FAILURE;
    }

    if(pid == 0)
    {   //Child Process
        execl("./db", "db", param0, param1, param2, param3, (char *)NULL);
    }
    else
    {   //Parent Process
        //SENDING VALUES HERE
        close(fd[P2_READ]);
        close(fd[P2_WRITE]);
        printf("Interface is sending|%d| to DBn", val);
        if(write(fd[P1_WRITE],&val, sizeof(val)) != sizeof(val))
        {
            perror("Interfae failed to send value to DB");
            exit(EXIT_FAILURE);
        }
    }
    return 0;
}

db.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/types.h>
//Typedef-Class-
typedef struct Information
{
    int accountId;
    int checkNumber;
    int date;
    float amount;
} Information;
int main(int argc, char *argv[])
{
//For Input
    //Account Data
    Information acctData[25];
    int dataStorageLooper = 0;      //How many db entries
    //For File Input
    int aVal;
    int bVal;
    int cVal;
    float dVal;
    //Prepare for file input:
    FILE * fp;
    fp = fopen ("accountData.txt", "r");
    //Reads Input
    while(1)
    {
        if (fscanf(fp, "%d %d %d %f", &aVal, &bVal, &cVal, &dVal)!=4)
        {
            break;
        }
        //Puts data into appropriate arrays
        acctData[dataStorageLooper].accountId= aVal;
        acctData[dataStorageLooper].checkNumber= bVal;
        acctData[dataStorageLooper].date= cVal;
        acctData[dataStorageLooper].amount= dVal;
        dataStorageLooper++;
    }
    //Decrement index to point to last item
    dataStorageLooper--;
    //Displays all values
    printf("nDisplaying AccountData.txtn");
    for( int i = 0; i < dataStorageLooper; i++)
    {
        printf("Line|%d|: Account|%d|: Check|%d|: Date|%d|: Amount|%.2f|n",i,acctData[i].accountId,acctData[i].checkNumber,acctData[i].date,acctData[i].amount);
    }
    //Closes File
    fclose(fp);
//End Input
//Parameter Receiving:
    int pipes[4];           //Pipe Array
    int value = 7;
    int test;
    //Build the pipes
    pipes[0] = atoi(argv[1]);       //P1_Read
    pipes[1] = atoi(argv[2]);       //P2_Write
    pipes[2] = atoi(argv[3]);       //P2_Read
    pipes[3] = atoi(argv[4]);       //P1_Write
    //Troubleshooting    
    printf("The number of parameters: %dn",argc);
    printf("Parameter 1: %sn", argv[0]);
    printf("I stared correctlyn");
    //Testing
    close(pipes[0]);
    close(pipes[3]);
    //SHOULD RECEIVE VALUE HERE
    test = read(pipes[2], &value, sizeof(value));
        if (test < 0)
        {
            perror("DB: Failed to read data from parent");
            exit(EXIT_FAILURE);
        }
        else if (test == 0)
        {
            //Unexpected
            fprintf(stderr, "DB: Read End-Of-File from pipe");
        }
        else
        {
            //What did the child receive?
            printf("DB: Received Value:(%d)n", value);
        }
        close(pipes[2]);
        close(pipes[1]);


    return 0;
}

Answer 1

您做错的事情之一是在您为fd分配任何值之前将CC_2中各种元素的值赋值。这是未定义的行为，你作为参数传递的值是完全没有意义的(充其量)。

我觉得这是一种非常奇怪的做事方式。通常，您只需将fds 0和1替换，以便将子节点的标准输入和标准输出重定向到适当的管道fds。