(re?)directing compile output to a file

[David Currie]

I am a musician and a programmer.

How does one redirect/direct (lilypond) compile output to a file and not stdout
using command line options(or otherwise).

One can double click filename.ly. 
It produces filename.log (which nicely contains errors etc).

BUT when (inside a c++ program)

 int result = spawnlp(P_WAIT,"lilypond","lilypond","filename.ly",NULL);
 
 It merely puts all output to a dos command prompt.
 Naturally it is so fast it cant be seen.
 Even upon failure (result == 1) there is no way to see errors

Incidently spawnlp(P_WAIT,"lilypond","lilypond",
       "c:\\someDirNotCurrent\\filename.ly",NULL);
  fails because it cant find "c:\\someDirNotCurrent\\filename.ly"
  this is not logical or if there is a workaround please advise

I use Windows 2000 professional. (forgive me) (Help please)

Thanks for any response, 
David