#include <iostream>
#include <cstdlib>

using namespace std;
int main()
{
 cout<<"1";
 sleep(1);
 cout<<"2";
 return 0;
}

g++ test.cpp -o test

fflush(STDIN)

scrat@scrat:/usr/include/c++/4.1.2$ ls
algorithm  clocale  ctime                functional      locale   stdexcept
backward   cmath    cwchar               i486-linux-gnu  map      streambuf
bits       complex  cwctype              iomanip         memory   string
bitset     csetjmp  cxxabi.h             ios             new      tr1
cassert    csignal  debug                iosfwd          numeric  typeinfo
cctype     cstdarg  deque                iostream        ostream  utility
cerrno     cstddef  exception            istream         queue    valarray
cfloat     cstdio   exception_defines.h  iterator        set      vector
ciso646    cstdlib  ext                  limits          sstream
climits    cstring  fstream              list            stack

$ ls /usr/include | grep uni
unistd.h