SysCall

パイプの仕組みについては名前なしパイプ(1)へ
ここでは, パイプを用いて足し算を行うプログラムやります.

                        #include<stdio.h>
#include<stdlib.h> // exit
#include<string.h> // strlen
#include<unistd.h> // fork

void error_message(const char *name);

int main(int argc, char **argv)
{
    pid_t pid;
    int na, nb, nc;
    int pa[2], pb[2];
    char buff[32], result[32];

    if(pipe(pa) == EOF || pipe(pb) == EOF)
        error_message("pipe");

    if((pid = fork()) == EOF)
        error_message("fork");

    else if(pid == 0) { //child process
        close(pa[1]);
        close(pb[0]);
        if(read(pa[0], buff, 32) == EOF)
            error_message("read");
        na = atoi(buff);

        if(read(pa[0], buff, 32) == EOF)
            error_message("read");
        nb = atoi(buff);

        nc = na + nb;

        sprintf(result, "%d", nc);

        if(write(pb[1], result, strlen(result) + 1) == EOF)
            error_message("write");

        printf("Child Process(PID:%d) Send Answer...\n", getpid());

        close(pa[0]);
        close(pb[1]);
    }

    else {
        close(pa[0]);
        close(pb[1]);

        printf("Parent Process(PID:%d)\n", getpid());
        printf("NumA:");
        fgets(buff, 32, stdin);
        if(write(pa[1], buff, strlen(buff) + 1) == EOF)
            error_message("write");

        printf("NumB:");
        fgets(buff, 32, stdin);
        if(write(pa[1], buff, strlen(buff) + 1) == EOF)
            error_message("write");

        if(read(pb[0], result, 32) == EOF)
            error_message("read");

        printf("Answer = %s\n", result);

        close(pa[1]);
        close(pb[0]);
    }

    return 0;
}

void error_message(const char *name) {
    perror(name);
    exit(EXIT_FAILURE);
}