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I've got a very simple program that just takes two unsigned int inputs, and then goes through a for loop reading out each number below 9 as: 

input 1 : output one

input 2 : output two

etc. and above 9 it outputs whether it is even or odd.

All goes fine except for when I call std::flush, it does not flush the buffer to the screen, however std::endl does. With the code as it is below, I get no output, however by changing flush to endl I do get an output. Why is this? I tried looking it up and all I could find slightly relevant was this Calls to flush cout are ineffective which said the problem was that a /r was being inserted, but I can't see how that could be the case here since I can see all the outputs don't have that.

#include <iostream>

enum integerState{belowTen,aboveNine};
enum parity{even,odd};

integerState process_integer(unsigned int n);
parity even_or_odd(unsigned int n);

int main(){
    unsigned int lowerLim,upperLim;
    std::cin >> lowerLim >> upperLim;
    for (unsigned int i=lowerLim;i<=upperLim;++i){
        process_integer(i);
    }

    return 0;
}

integerState process_integer(unsigned int n){

    switch(n){
        case 1: std::cout << "one" << std::flush;                   return belowTen;
        case 2: std::cout << "two" << std::flush;                   return belowTen;
        case 3: std::cout << "three" << std::flush;                 return belowTen;
        case 4: std::cout << "four" << std::flush;                  return belowTen;
        case 5: std::cout << "five" << std::flush;                  return belowTen;
        case 6: std::cout << "six" << std::flush;                   return belowTen;
        case 7: std::cout << "seven" << std::flush;                 return belowTen;
        case 8: std::cout << "eight" << std::flush;                 return belowTen;
        case 9: std::cout << "nine" << std::flush;                  return belowTen;
        default: 
        if(even_or_odd(n)==even){ std::cout << "even" << std::flush; return aboveNine;}
        if(even_or_odd(n)==odd){  std::cout << "odd"  << std::flush; return aboveNine;}
        return aboveNine;
    }
}

parity even_or_odd(unsigned int n){
    return (n%2==0 ? even:odd);
}

I'm using g++ if that matters.

Thanks

John Cunningham
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    How can you tell it's not working? When the program ends, all output will be flushed, so you can't tell if it's flushing in the middle or between each number. – Barmar Jul 30 '17 at 22:26
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    I tried your program, I got output. – Barmar Jul 30 '17 at 22:27
  • @Barmar because it does not flush at any point including when the program ends. without std::endl there is no output to the console. – John Cunningham Jul 30 '17 at 22:41
  • Can not reproduce. Your code works for me. I get output as expected. – Galik Jul 30 '17 at 22:56
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    `flush` just ensures the data is send out of the C++ program; the host environment might do its own line buffering – M.M Jul 30 '17 at 23:28

0 Answers0