printf not printing on console - c

Question

I’m getting started in the C language. I am using eclipse (juno) as my IDE and installed CDT plugin. I have also unpacked mingw64 (GCC Compiler). I wrote a very simple program to see if it works. This is my code:
#include <stdio.h>
int main()
{
int age;
printf("Hello, please enter your age:\n");
scanf("%d", &age);
printf("Your age is %d", age);
return 0;
}
The problem is that the output buffer is filled with the string value of the first printf but does not output it to the console. I have to enter a number, and only then the buffer pours all the data to the console so I see the console something like this:
1
Hello, please enter your age:
Your age is 1
instead of what is expected that is:
Hello, please enter your age:
1
Your age is 1
Now, I found that I can use fflush(stdout) after the first printf but I don't think that this solution is elegant and even necessary. Any ideas on how I can overcome this?
EDIT - because I'm learning this in my university, I can't use anything that wasn't learned in the course so I can only use printf and scanf
NEW EDIT - I think I have found an explanation for this. As I said, I am outputting to the console view inside Eclipse. The strange thing is that if I compile and run the program from the command line of Windows, I get the wanted result. Therefore, I think that eclipse is actually writing the output to a file and presenting it in the console window. How can I force eclipse to open a real command line window in my run configurations?

Answer 1

Output is buffered.
stdout is line-buffered by default, which means that '\n' is supposed to flush the buffer. Why is it not happening in your case? I don't know. I need more info about your application/environment.
However, you can control buffering with setvbuf():
setvbuf(stdout, NULL, _IOLBF, 0);
This will force stdout to be line-buffered.
setvbuf(stdout, NULL, _IONBF, 0);
This will force stdout to be unbuffered, so you won't need to use fflush().
Note that it will severely affect application performance if you have lots of prints.

Answer 2

Apparently this is a known bug of Eclipse. This bug is resolved with the resolution of WONT-FIX. I have no idea why though. here is the link:
Eclipse C Console Bug.

Answer 3

You could try writing to stderr, rather than stdout.
fprintf(stderr, "Hello, please enter your age\n");
You should also have a look at this relevant thread.

Answer 4

Try setting this before you print:
setvbuf (stdout, NULL, _IONBF, 0);

Answer 5

As others have pointed out, output can be buffered within your program before a console or shell has a chance to see it.
On unix-like systems, including macs, stdout has line-based buffering by default. This means that your program empties its stdout buffer as soon as it sees a newline.
However, on windows, newlines are no longer special, and full buffering is used. Windows doesn't support line buffering at all; see the msdn page on setvbuf.
So on windows, a good approach is to completely shut off stdout buffering like so:
setvbuf (stdout, NULL, _IONBF, 0);

Answer 6

Add c:\gygwin\bin to PATH environment variable either as a system environment variable or in your eclipse project (properties-> run/debug-> edit)

Answer 7

In your project folder, create a “.gdbinit” text file. It will contain your gdb debugger configuration
Edit “.gdbinit”, and add the line (without the quotes) : “set new-console on”
After building the project right click on the project Debug > “Debug Configurations”, as shown below
In the “debugger” tab, ensure the “GDB command file” now points to your “.gdbinit” file. Else, input the path to your “.gdbinit” configuration file :
Click “Apply” and “Debug”. A native DOS command line should be launched as shown below