Clearing the cout buffer (c++) - c++

Question

Hello I'm writing a short program to implement a shell and I'm running into an unusual problem. For some reason I can't clear to the std::cout buffer. The program wont print out messages. I understand a simple solution is to switch to std::cerr, but is there a way to get messages to print with cout?
Things I've tryed:
std::cout.flush()
Inserting std::endl after anything is written to standard out.
Inserting an std::flush into the output stream
std::cout.setf(std::ios::unitbuf); which was something I found that should unbuffer output.
Any help is much appreciated here is my code:
int main()
{
//Tryed this to unbuffer cout, no luck.
std::cout.setf(std::ios::unitbuf);
std::string input;
//Print out shell prompt and read in input from keyboard.
std::cout << "myshell> ";
std::getline(std::cin, input);
//**********************************************************************
//Step 1) Read in string and parse into tokens.
//**********************************************************************
char * buf = new char[input.length() + 1];
strcpy(buf, input.c_str());
int index = 0;
char * command[256];
command[index] = std::strtok(buf, " "); //Get first token.
std::cout << command[index] << std::endl;
while (command[index] != NULL)
{
++index;
command[index] = std::strtok(NULL," "); //Get remaining tokens.
std::cout << command[index] << std::endl;
}
std::cout.flush(); //No luck here either
//HERE IS WHERE MY PROBLEM IS.
std::cout << index << " items were added to the command array" << std::endl;
delete[] buf;
return 0;
}

Answer 1

The problem is that you're sending NULL to cout on the last iteration of the while loop, which leads to UB, and in your case is jamming cout. Check for NULL before you send anything to cout and you're fine:
if (command[index] != NULL) {
std::cout << command[index] << std::endl;
}

Answer 2

If you ever need to know what happened to your streams, remember that they can carry status information (the iostate, which I recommend you read about). The following code could have helped track your error:
try {
std::cout.exceptions(std::cout.failbit);
} catch(const std::ios_base::failure& e) {
std::cerr << "stream error: " << e.what() << std::endl;
std::cout.clear();
}
// continue working with cout, because std::cout.clear() removed
// failbit
Or, even simpler:
if(not std::cout) {
// address your error (if it is recoverable)
}
This is how your code would have looked like:
#include <cstring>
#include <string>
#include <iostream>
int main()
{
//Tryed this to unbuffer cout, no luck.
std::cout.setf(std::ios::unitbuf);
std::string input;
//Print out shell prompt and read in input from keyboard.
std::cout << "myshell> ";
std::getline(std::cin, input);
//**********************************************************************
//Step 1) Read in string and parse into tokens.
//**********************************************************************
char * buf = new char[input.length() + 1];
strcpy(buf, input.c_str());
int index = 0;
char * command[256];
command[index] = std::strtok(buf, " "); //Get first token.
std::cout << command[index] << std::endl;
while (command[index] != NULL)
{
++index;
command[index] = std::strtok(NULL," "); //Get remaining tokens.
std::cout << command[index] << std::endl;
}
// I added from here...
if(not std::cout) {
std::cerr << "cout is messed up... fixing it..." << std::endl;
std::cout.clear();
}
// ... to here.
std::cout.flush(); //No luck here either
//HERE IS WHERE MY PROBLEM IS.
std::cout << index << " items were added to the command array" << std::endl;
delete[] buf;
return 0;
}
Result:
$ ./a.out
myshell> 1 2 3
1
2
3
cout is messed up... fixing it...
3 items were added to the command array