GDB console can't show the result of printf

Question

I'm using gdb in RedHat to debug C++ code. To better debug my code, I added printf("XXX").

However, after the execution of printf("XXX"), the gdb console didn't show XXX.

Other parts of my code works fine.

Answer 1

It's likely that your output is line-buffered, and because you didn't end the print with a newline, the output hasn't been flushed. Three easy fixes:

1. std::printf("XXX"); std::fflush(stdout);
2. std::printf("XXX\n");
3. std::puts("XXX");

Also, take care if you're mixing C-style FILE* i/o with C++-style streams.