c - 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 - 不是完美的英语!)

在拼贴画上，他们给了我一个任务，我苦苦挣扎了几个小时，却无法解决。 我在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，但我没有从子进程接收到它。你们能帮忙吗？

程序描述:我的工作是从用户那里获取输入，使用管道将其发送到子进程，进行一些计算，然后将这些计算进一步发送到下一个进程。最后一个过程对传入的数据求和并将其分配给最终结果。更具体地说，第一个子进程计算麦克劳林级数的单项并将其发送给对其求和的进程。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;

}

这里是代码的结果:

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，我解决了那个问题，程序给了我预期的结果。第一个关键要素是删除

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

就像 Jonathan Leffler 所说 *“在你的程序中包含 int mkfifo(const char s, mode_t m) { return 0; } 意味着你不会创建 FIFO，所以你不能使用它们。你需要删除它以使用系统调用。”

第二件事是支持我的 fifo 在 lseek() 函数单次使用后一遍又一遍地开始。我还必须在使用 memset() 后清除所有缓冲区。

现在这是我的代码:

#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;

}

现在我可以看到使用麦克劳林级数对 e^x 函数进行数学估计的美妙之处。以下是结果:

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

估计满意:)