c - pipe chain between processes -

c - pipe chain between processes -

i want have 1 parent 2 children.

the parent reads file "a.txt" , sends trough pipe first child; first kid reads chars , sends sec kid lower letter chars.

the sec kid prints in "b.txt" each distinct char , number of appearances(per line) , sends trough pipe parent number of distinct chars. parent prints result sec child.

i've done pipe parent 1 kid , test i've set pipe parent. can't figure out how create pipe go sec child. i've been searching info on dup2 don't on how create work.

#include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/wait.h> #include <unistd.h> #include <ctype.h> #include <fcntl.h> void main() { int pfd1[2], pfd2[2], pid1, pid2, pfin, status, fd; char *c = (char *)malloc(sizeof(char)); if (pipe(pfd1) < 0) { printf("eroare la crearea pipe-ului\n"); exit(1); } if (pipe(pfd2) < 0) { printf("eroare la crearea pipe-ului\n"); exit(1); } if ((pid1 = fork()) < 0) { printf("eroare la fork\n"); exit(1); } if (pid1 == 0) { /*child */ close(pfd1[1]); while (read(pfd1[0], c, 1) > 0) { //printf("%s",c); if (islower(*c)) { close(pfd2[0]); //inchid capul de citire; scriu in pipe write(pfd2[1], c, 1); ////dup?????? } } printf("\n"); write(pfd[1], buff, len); close(pfd1[0]); close(pfd2[1]); exit(0); } if ((pid2 = fork()) < 0) { printf("eroare la fork\n"); exit(1); } if (pid2 == 0) { printf("second child"); exit(0); } /* parent */ close(pfd1[0]); close(pfd2[1]); fd = open("date.txt", o_rdonly); while (read(fd, c, 1) > 0) { write(pfd1[1], c, 1); } close(pfd1[1]); /* la sfarsit inchide si capatul utilizat */ close(pfin); while (read(pfd2[0], c, 1) > 0) printf("%s", c); close(pfd2[0]); printf("%d", wait(&status)); printf("%d", wait(&status)); }

i have few specific comments on code:

char *c = (char *)malloc(sizeof(char));

while there nil wrong this, there no need char allocated heap. more idiomatic approach utilize char c; here , pass &c read(2) , write(2) scheme calls. (even more idiomatic utilize c standard io facility; freopen(3), getchar(3), , putchar(3) -- not create transition until have code working want to, because additional complication problem you're trying solve.)

if ((pid1 = fork()) < 0) { printf("eroare la fork\n"); exit(1); }

by using own error message, missing out on of import error information. should utilize perror(3) print error message instead. give , users actual cause errors can search for. fork(2) can fail if user running setrlimit(2) nproc maximum process limit, system-wide process limit, out of kernel memory.

if ((pid1 = fork()) < 0) { perror("eroare la fork"); exit(1); }

you should check homecoming value open(2) calls. (you're supposed check homecoming values write(2) , close(2) errors, handling these errors harder. printing error , quitting start programs.)

while (read(pfd1[0], c, 1) > 0) { //printf("%s",c); if (islower(*c)) { close(pfd2[0]);

this wrong location close(2) phone call -- shouldn't closing filedescriptor on , on every input character. if checking close(2) homecoming value, notice errno set ebadf because file descriptor no longer valid on sec , subsequent calls.

now, onto problem came here for: sequence of fork(), pipe(), , dup2() calls hook processes in pipeline , send info parent process. since pipe(2) creates uni-directional pipe(7)s, need phone call pipe(2) four times -- both directions between parent , children. if store pipe endpoints in arrays names mean you, easier maintain track of. perhaps create arrays named to_ writing , from_ reading from:

int to_child[2]; int from_parent[2]; int to_parent[2]; int from_child[2]; (int i=0; i<2; i++) { int p[2]; if (pipe(p) == -1) { perror("pipe"); exit(1); } /* parent kid */ to_child[i] = p[1]; from_parent[i] = p[0]; if (pipe(p) == -1) { perror("pipe"); exit(1); } /* kid parent */ to_parent[i] = p[1]; from_child[i] = p[0]; }

note don't need utilize dup2(2) re-arrange filedescriptors unless want execute other programs handle "filter" task. read(2) using from_parent[...] or from_child[...] descriptors , write(2) to_child[...] , to_parent[...] descriptors.

maybe entire thing easier socketpair(2) using af_unix create bi-directional sockets, can read , written in same fashion other bsd-style socket. see socket(7) , unix(7) overview.

c pipe dup2