Duplicate stdout and stderr from fork process to files

Question

I need to duplicate stdout and stderr of a child proccess to multiple files.
I understand that i can use tee(), but I haven't found examples for that. Now, it's only to print all to stdout and stderr. How to do it?

 pid_t childId = fork();
    switch(childId){
    case -1:
        perror("fork() error!\n");
        return;
    case 0:

        mysignal(SIGTTOU, SIG_DFL);
        mysignal(SIGTTIN, SIG_DFL);
        mysignal(SIGCHLD, SIG_DFL);
        if(!background)
            tcsetpgrp(cterm, getpid());
        setpgid(0, 0);
        if (isWriter) close(pipefd[0]);
        if (isReader!=-1) {
            close(0);
            dup(oldChannelOut);
        }

        if(isWriter){
            close(1);
            dup(pipefd[1]);
        }
        //exec, if program is in current directory
        execv(commandArgv[0], commandArgv);
        int i = 0;
        char buf[_POSIX_MAX_PATH];
        while(path[i] != NULL){
            buf[0] = '\0';
            strcat(buf, path[i]);
            if(path[i][ strlen(path[i])-1 ] != '/'){
                buf[strlen(path[i])] = '/';
                buf[strlen(path[i])+1] = '\0';
            }
            strcat(buf, commandArgv[0]);
            execv(buf, commandArgv);
            ++i;
        }
        fprintf(stderr,"\"%s\": command not found\n",commandArgv[0]);
        exit(1);

UPD: After tried modify, dont work. Where is problem ?

fdout=open("1", O_APPEND | O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
fderr=open("2",O_APPEND | O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
...
case 0:
if (isReader!=-1) {
close(0);
dup(oldChannelOut);
}
dup2(fdout, 1);
dup2(fderr, 2);
close(fdout);
close(fderr);
 exec....
default:
{

if(background) {
addJob(&jobListStartB,childId,commandArgv,BACKGROUND);
if (oldChannelOut != -1){
close(oldChannelOut);
oldChannelOut = -1;
}
}
else if(!background){
if (oldChannelOut != -1){

close(oldChannelOut);
oldChannelOut = -1;
}
} 

Answer 1

Using tee and splice to write data from a handle to multiple other handles:

// Needs at least two targets, sentinel is INVALID_HANDLE_VALUE
int push_to_all(int source, ssize_t count, ...) {
    va_list vl;
    va_start(vl, count);
    int target = va_arg(vl, int), next = va_arg(vl, int);
    count = tee(source, target, count, SPLICE_F_NONBLOCK);
    if(count <= 0) { va_end(vl); return count; }
    while((target = next, next = va_arg(vl, int)) > 0) {
        tee(source, target, count, 0);
    va_end(vl);
    return splice(source, 0, target, 0, count, 0);
}