Problem with Debugging in Eclipse CDT

Question

I'm trying to debug the simple Hello World program that ships with Eclipse CDT. Running the program normally works fine, but when its run through debug mode, puts() doesn't print anything to the console.

I tried running the same program with gdb directly and it works fine, printing "!!!Hello World!!!" as expected.

Why doesn't puts() print anything when running in debug mode through Eclipse?

I'm on Windows with MinGW installed, running gcc 4.5.0, gdb 7.2, and CDT 7.0.1

Answer 1

Have you tried to append \n in the puts statement? I.e. puts("Hello World!\n"); Some times terminal needs \n to flush the stream.

Answer 2

I figured out why this happens. When running GDB through a terminal, STDOUT is line buffered, which means that it will be flushed every time a newline is read, resulting in the behavior I was expecting.

HOWEVER! Eclipse CDT runs GDB with STDOUT in block buffered mode, which means it will only flush STDOUT when it reaches a certain size, or if it is manually flushed. Since the string "!!!Hello World!!!" is so short, the buffer for STDOUT will never be flushed unless a call to fflush() is made.

I managed to fix this problem by adding fflush(stdout); after the call to puts().

Here's the resulting code:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    puts("Hello World!"); /* prints !!!Hello World!!! */
    fflush(stdout);
    return EXIT_SUCCESS;
}