Input redirection in gdb (MinGW)

Solution 1:

As far back as the late '90s, broken command line redirection was a known and assumed limitation. My suspicion is that it remains that way, since the mingw32 port of gdb still gleefully passes on verbatim all run arguments (including redirects) to the debugee.

Several possible workarounds:

1. if you have the option to alter the command line interface, then implement bbadour's suggestion
2. otherwise, if you can easily suspend the process before the point you want to debug at, invoke the debugee (with redirection) from a shell and attach to it while it is already running

3. otherwise, if you have symbols for the debugee (gcc -g) or you know the address of main() (gcc -Wl,-Map,mapfile) and can set a breakpoint there, proceed in the following manner (tested with mingw gdb 6.8.0):

   # gdb debugee.exe
   (gdb) b main
   (gdb) run non-redirect-arguments-if-any
   (gdb) p dup2(open("/tmp/input.txt", 0), 0) 
   (gdb) c
   

Solution 2:

I ran into the same issue here, and I just got into the habit of adding a command-line argument to allow grabbing input from a file.

e.g. Parsing a "-i ifile" argument using argc and argv to get input from ifile instead of stdin and parsing a "-o ofile" to write output to ofile instead of stdout.

Then I just use those arguments instead of redirects.

The tools that come with MinGW often are not the latest versions and often have features omitted. ::shrug::