dup() creating file but not printing to it - c++

Question

I am trying to create a shell in c++. It creates a child process which executes a command and pipes the response back to the parent. I want to specify if the second argument of a command is -o then I would like to redirect the output of the command to a file. (output.txt).I used dup() to redirect output to my file. However, when I run the program and enter for example wc -o fileName the program creates the file output.txt but does not write to it when I specify to print the result of my child process.
#include <iostream>
#include <unistd.h>
#include <stdio.h>
#include <cstring>
#include <fcntl.h>
#include <vector>
#include <sys/wait.h>
int main(){
// array of file descriptors for parent and child
int filedes[2];
char foo[4096];
char** argv;
std::cout << "$$-> ";
char command[128];
std::cin.getline(command, 128);
if(strlen(command) != 0) {
std::vector<char *> args;
char *prog = strtok(command, " ");
char *tmp = prog;
while(tmp != NULL) {
args.push_back(tmp);
tmp = strtok(NULL, " ");
}
argv = new char *[args.size() + 1];
for (int k = 0; k < args.size(); k++) {
argv[k] = args[k];
}
argv[args.size()] = NULL;
}
char* newargc = argv[0];
char *newargv[] = {newargc,argv[2],NULL};
if(pipe(filedes) < 0){
std::cout << "There was an error creating the pipe";
}
int pid = fork();
if(pid == 0){
// writing to the pipe
// close read end of pipe
close(filedes[0]);
close(STDOUT_FILENO);
dup(filedes[1]);
if(strcmp(argv[1],(char*)"-o") == 0 ||strcmp(argv[1], (char*) "-b") == 0){
execvp(newargv[0], newargv);
}
else{
execvp(argv[0],argv);
}
}
else if (pid > 0) {
std::cout << "This is the parent process\n";
while(wait(NULL) > 0);
close(filedes[1]);
int output_fd = open("output.txt", O_CREAT, O_TRUNC, O_RDWR);
read(filedes[0], foo, sizeof(foo));
if(strcmp(argv[1],(char*)"-o") == 0){
close(STDOUT_FILENO);
dup(output_fd);
write(output_fd, foo, sizeof(foo));
}
else if(strcmp(argv[1], (char*) "-b") == 0){
int stdoutHolder = dup(STDOUT_FILENO);
close(STDOUT_FILENO);
dup(output_fd);
std::cout<< foo;
dup2(stdoutHolder, 1);
}
std::cout << foo;
}
//pid is less than 0 if error
else{
std::cout << "There is an error.";
}
return 0;
}