Linux。 C中的管道。将数据发送到另一个进程。 写作和阅读

Question

（警告-不完美的英语！）

在拼贴上，他们给了我一个任务，而我奋斗了几个小时而无法解决。 我将数据从一个进程发送到另一个进程时遇到问题。 在下面的代码中，我将输入数据发送到子进程，但未从子进程接收它。 你们可以帮忙吗？

程序说明：我的工作是从用户那里获取输入，使用管道将其发送到子流程，进行一些计算，然后将此计算进一步发送到下一个流程。 最后一个过程对输入的数据求和，并将其分配给最终结果。 更具体地说，第一个子进程计算Maclaurin系列的单个术语，并将其发送给求和的过程。 这是代码：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <math.h>
#include <sys/stat.h>

int mkfifo(const char *s, mode_t m) {
  return 0;
}

 int i = 1;
 double FINAL_RESULT = 0 ;


double factorial(int N){

    if(N==1)return 1.0;

    return N*factorial(N - 1);

}
double Maclaurine(int i , double x , double eps){

    double result;

     result = (pow(x,(double)i) / (double)factorial(i));

    if( result < eps) return 0;

    return result;

}

void print(char * tab, int size){

    printf("\n");   

    for( int i = 0; i < size ; i++){

        printf("%c" , tab[i]);  

    }   
    printf("\n");   
}



int main(){

    int pd;

    if(mkfifo("tmp/myfifo1", 0666) == -1){

        printf("Failed to create myfifo2\n");
    }

    if(mkfifo("tmp/myfifo2", 0666) == -1){

        printf("Failed to create myfifo2\n");

    }

    pd = open("tmp/myfifo1", O_WRONLY);

    double x1,eps1;

    printf("X Value : \n");
    scanf("%lf", &x1);
    printf("EPS Value : \n");
    scanf("%lf", &eps1);

    char tab1[128], tab2[128];

    //converting to char*
    sprintf(tab1,"%lf",x1);
    sprintf(tab2,"%lf",eps1);

    //printing to standard output
    print(tab1, strlen(tab1));
    print(tab2, strlen(tab2));

    //creating new process
    if(fork() == 0){

        //creating another process
        if(fork() == 0){

            int pd3; 
            pd3 = open("tmp/myfifo2", O_RDONLY);

            char tab5[128];

            double x3;

            //reading data from pipe , myfifo2
            read(pd3,tab5,sizeof(tab5));

            //converting char* to float
            x3 = atof(tab5);

            FINAL_RESULT += x3;
            printf("\nCurrent result = %lf" , FINAL_RESULT);

        }
        int pd2;
        //opening myfifo1 for reading 
        pd2 = open("tmp/myfifo1", O_RDONLY);

        if(pd2 == - 1){

            printf("\nFailed to open myfifo1 for reading!\n");

        }
        double x2, eps2;
        char tab3[128], tab4[128];

        //reading inputed parameters        
        read(pd2,tab3, sizeof(tab3) );

        read(pd2,tab4, sizeof(tab4) );
        //converting to floats
        x2 = atof(tab3);

        eps2 = atof(tab4);

        printf("\nReceived initial data x=%f, eps = %f \n" , x2, eps2);

        double singleTerm = 0;

        int pd4;

        char wyraz[128];

        //opening myfifo2 for writing 
        pd4 = open("tmp/myfifo2", O_WRONLY);

        if(pd4 == -1 ){
            printf("\nfailed to open myfifo2\n");
        }

        do{
            //calculate single term of Maclaurin series
            singleTerm = Maclaurine(i,x2,eps2);
            printf("\n%d. Series term = %lf\n", i,singleTerm);

            sprintf(wyraz,"%lf",singleTerm);

            if(write(pd4, wyraz, sizeof(wyraz)) == -1 ){
                printf("\nfailed to send singleTerm to myfifo2\n");
            }

            i++;
            //if its less than eps, loop ends
        }while(singleTerm);

        printf("\nFinal Result :  %lf", FINAL_RESULT);
        close(pd4);
        close(pd2);

        unlink("tmp/myfifo2");

    }

    //write data to myfifo1
    write(pd, tab1, sizeof(tab1));

    write(pd, tab2, sizeof(tab2));

    close(pd);

    unlink("tmp/myfifo1");

    return 0;

}

这是代码的结果：

pawel@IMPERIUMVB:~$ gcc pipes.c -lm -o x
pawel@IMPERIUMVB:~$ ./x
X Value : 
10
EPS Value : 
0.001

10.000000
0.001000

pawel@IMPERIUMVB:~$ 
Failed to open myfifo1 for reading!
Received initial data x=0.000000, eps = 0.000000 
failed to open myfifo2
1. Series term = 0.000000
failed to send singleTerm to myfifo2
Final Result :  0.000000
Current result = 0.000000
Failed to open myfifo1 for reading!
Received initial data x=0.000000, eps = 0.000000 
failed to open myfifo2
1. Series term = 0.000000
failed to send singleTerm to myfifo2
Final Result :  0.000000

Answer 1

好的，我解决了这个问题，程序给了我预期的结果。 第一个关键要素是擦除

int mkfifo(const char *s, mode_t m) { return 0; }

就像乔纳森·莱夫勒（Jonathan Leffler）所说的*“在程序中包含int mkfifo（const char s，mode_t m）{return 0;}意味着您将不会创建FIFO，因此无法使用它们。您需要将其删除才能使用系统呼叫。”

第二件事是通过lseek（）函数一次又一次地支持我的fifo。 另外，使用memset（）后，我还必须清除所有缓冲区。

现在是我的代码：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <math.h>
#include <sys/stat.h>



 int i = 0;
 double FINAL_RESULT = 1.0 ;


double factorial(int N){

    if(N==1 || N == 0)return 1.0;

    return N*factorial(N - 1);

}
double Maclaurine(int i , double x , double eps){

    double result;

     result = (pow(x,(double)i) / (double)factorial(i));

    if( result < eps) return -1.0;

    return result;

}

void print(char * tab, int size){

    printf("\n");   

    for( int i = 0; i < size ; i++){

        printf("%c" , tab[i]);  

    }   
    printf("\n");   
}



int main(){

    umask(0);

    if(mkfifo("myfifo1", 0666) == -1){

        printf("Failed to create myfifo2\n");
    }

    if(mkfifo("myfifo2", 0666) == -1){

        printf("Failed to create myfifo2\n");

    }


    if(fork() == 0){

        int pd = open("myfifo1", O_WRONLY);

        double x1,eps1;
        char tab1[256];
        //assigning tab1 data to 0's

        lseek(pd,0,0);
        memset(tab1, 0, 256);

        printf("X Value : \n");
        scanf("%lf", &x1);


        sprintf(tab1,"%lf",x1);
        //write data to myfifo1
        write(pd, tab1, strlen(tab1));

        printf("EPS Value : \n");
        scanf("%lf", &eps1);

        lseek(pd,0,0);
        memset(tab1, 0, 256);

        //converting to char*
        sprintf(tab1,"%lf",eps1);


        write(pd, tab1, strlen(tab1));

        lseek(pd,0,0);
        memset(tab1, 0, 256);

        close(pd);

        unlink("myfifo1");


        //printing to standard output
        //print(tab1, strlen(tab1));
        //print(tab2, strlen(tab2));

        //creating new process
    }
    else if(fork() == 0){


        int pd2, pd3;
        //opening myfifo1 for reading 
        pd2 = open("myfifo1", O_RDONLY);
        //opening myfifo2 for writing 
        pd3 = open("myfifo2", O_WRONLY);



        if(pd2 == - 1){
            printf("\nFailed to open myfifo1 for reading!\n");
        }


        if(pd3 == -1 ){
            printf("\nfailed to open myfifo2\n");
        }

        double x2, eps2;
        char tab2[256];

        lseek(pd2,0,0);
        memset(tab2, 0, 256);

        //reading inputed parameters        
        read(pd2,tab2, sizeof(tab2) );

        //converting to floats
        x2 = atof(tab2);

        lseek(pd2,0,0);
        memset(tab2, 0, 256);

        read(pd2,tab2, sizeof(tab2) );
        //converting to floats

        eps2 = atof(tab2);

        lseek(pd2,0,0);
        memset(tab2, 0, 256);

        //printf("\nReceived initial data x=%f, eps = %f \n" , x2, eps2);

        double singleTerm = 0.0;


        char wyraz[256];



        while(1){

            //calculate single term of Maclaurin series

            singleTerm = Maclaurine(i,x2,eps2);

            if(singleTerm > 0.0)printf("\n%d. Term of Mac Series = %lf", i+ 1,singleTerm);

            sprintf(wyraz,"%lf",singleTerm);


            lseek(pd3,0,0);

            if(write(pd3, wyraz, sizeof(wyraz)) == -1 ){
                printf("\nfailed to send singleTerm to myfifo2\n");
            }
            if(singleTerm < 0.0){

            //printf("\nI just broke the 1 loop\n");
            memset(wyraz, 0, 256);
            break;
            }


            i=i+1;
        }
        sleep(1);


        close(pd3);
        close(pd2);

        unlink("myfifo2");
        unlink("myfifo1");

    }//creating another process
    else if(fork() == 0){

            int pd4; 
            pd4 = open("myfifo2", O_RDONLY);

            char tab3[256];

            double x3 = 0.0;

            while(1){

            x3=0.0;
            lseek(pd4,0,0);
            memset(tab3, 0, 256);
            //reading data from pipe , myfifo2
            read(pd4,tab3,sizeof(tab3));

            //converting char* to float
            x3 = atof(tab3);

            FINAL_RESULT += x3;


            if(x3<=0.0){

            printf("\nFinal Result :  %lf", FINAL_RESULT ); 
            break;}
            //else
            //printf("\n x = %lf, Current result = %lf" ,x3, FINAL_RESULT);
            }

            sleep(1);

            printf("\nFinal Result :  %lf", FINAL_RESULT);

            close(pd4);
            unlink("myfifo2");

        }

    sleep(7);
    unlink("myfifo1");
    unlink("myfifo2");

    while(1)pause();

    return 0;

}

现在，我可以使用Maclaurin系列看到e ^ x函数的数学估计的美妙之处。 结果如下：

pawel@IMPERIUMVB:~$ gcc rury.c -lm -o zad1
pawel@IMPERIUMVB:~$ ./zad1
X Value : 
8
EPS Value : 
0.0001

1. Term of Mac Series = 1.000000
2. Term of Mac Series = 8.000000
3. Term of Mac Series = 32.000000
4. Term of Mac Series = 85.333333
5. Term of Mac Series = 170.666667
6. Term of Mac Series = 273.066667
7. Term of Mac Series = 364.088889
8. Term of Mac Series = 416.101587
9. Term of Mac Series = 416.101587
10. Term of Mac Series = 369.868078
11. Term of Mac Series = 295.894462
12. Term of Mac Series = 215.195972
13. Term of Mac Series = 143.463982
14. Term of Mac Series = 88.285527
15. Term of Mac Series = 50.448873
16. Term of Mac Series = 26.906065
17. Term of Mac Series = 13.453033
18. Term of Mac Series = 6.330839
19. Term of Mac Series = 2.813706
20. Term of Mac Series = 1.184718
21. Term of Mac Series = 0.473887
22. Term of Mac Series = 0.180529
23. Term of Mac Series = 0.065647
24. Term of Mac Series = 0.022834
25. Term of Mac Series = 0.007611
26. Term of Mac Series = 0.002436
27. Term of Mac Series = 0.000749

Final Result :  2980.957900 // after adding all of above

e ^ 8〜2980.9579870417

估计令人满意：)