gdb input redirection using cygwin

Question

It seems that input redirection in gdb does not work in Cygwin e.g

(gdb) run < input.txt

Is there other way to redirect input in gdb of Cygwin??

Answer 1

Unfortunately this is not possible when running gdb in cygwin. The bug exists for a quote long time, but apparently it's a hard one to fix - and probably the gdb devs prefer spending time on features/issues relevant to more common environments (such as Linux).

There are various possible workarounds; I'd prefer the first one since it's the cleanest and also useful while not debugging / running on cygwin:

• Add a command line argument, e.g. -f whatever with whatever being the filename to read from. If the argument is not present or set to -, read from stdin. The -f - option is optional of course but for arguments accepting filenames it's a common standard (as long as it makes sense) to handle - as "use stdin/out".

• Use the gdb hack mentioned here to remap stdin to a manually opened file inside the application:

  > gdb yourexecutable
  (gdb) break main
  (gdb) run
  (gdb) call dup2(open("input.txt", 0), 0)
  (gdb) continue
  

  This sets a breakpoint on the main function, then executes the program which will break right after entering main. Then dup2 is used to replace the stdin fd (0) with a file descriptor of the input file.