I have some C code using fork but I don't understand how it works
int hijo,i,N; int main(int argc, char*argv[]){ N=atoi(argv[1]); for(i=0;i<N;i++) if((hijo=fork())>0)break; } Why does this program create only one child process of the previously created process and doesn't create a process for each of the processes that exist before do the fork?
The code is equal to this:
int hijo; int main(int argc, char*argv[]){ if (argc < 2) return 1; // let's not crash // assume i and N are global variables not shown... N=atoi(argv[1]); i = 0; if (N < 1) return 0; // do not enter loop if N < 1 do { hijo=fork(); } while (hijo <= 0 && ++i < N); } From this we can more easily see, that for the original parent process, where hijo value is the pid of the first child, the loop condition is false immediately, and loop ends.
Same repeats for every child process, so a process can only be parent (hijo > 0) for one forked process.
N? 2: It's unclear what you're asking; are you wondering why the children don't fork too?printf()traces that help understand which process execute which part of code.pid=fork(); if(pid==0) {/*Child code*/} else{ wait()}this last wait() is important to not leave any zombie child because childs would be running on background forever if the child program does not end.