Put the exe name in quotes, too: 
"D:\Program Files\foo.exe" arg1 arg2 "file_name with spaces.txt"

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The logic of system's argument processing is supposed to make sense on Unix, with underlying OS primitives that work in the same way. But it's a mess on Windows, where the documented meaning is implemented to some degree. Point is, it takes different code paths depending on the form, with different behavior. It's been a while since I looked at it. But if it calls the CMD.exe shell with the whole thing as a string, it behaves the same way as on the command line, as I showed. If it tries to call CreateProcess directly, the exe file name is a separate argument to that.

I suppose I should refresh my knowledge before writing anything that makes use of that feature myself.

In reply to Re^3: quoting issue with system command by John M. Dlugosz
in thread quoting issue with system command by lomSpace

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