On 20/07/2026 12:02, Marco van de Voort via fpc-pascal wrote:
Op 20-7-2026 om 11:57 schreef Michael Van Canneyt via fpc-pascal:
I am looking at the implementation of POpen and PClose in the
runtime-library for Darwin (or more general for UNIX). It seems
like it doesn't call into libc popen and pclose, but instead
follows its own implementation in unix.pp in POpen_internal. I am
just curious to know the reason.
Phew, that was over twenty years ago, but afaik the reason is that
libc popen and pclose us C FILE descriptors, which the RTL in
general doesn't use to avoid a mix of functions with pascal and C
file types.
So popen/pclose are a more high level (FILE * using) part of libc,
while we tend to only use the basis.
Glad our memories agree on this :-)
Well aside from the fact that FreeBSD was the architecture where the
baseunix/unix RTL was done. The port to Linux was only done later :-)
This shows the tension a bit between libc the system lib, and libc the
C runtime. We are only interested in the system lib part.
Another question. POpen has a file as input parameter. The description
in unix.pp says
"Starts the program in 'Prog' and makes it's input or out put the
other end of a pipe. If rw is 'w' or 'W', then whatever is written to
F, will be read from stdin by the program in 'Prog'. The inverse is true
for 'r' or 'R' : whatever the program in 'Prog' writes to stdout, can be
read from 'f'."
So, for write mode, it doesn't use StdOut but a file. Does this imply
that (for writing) I can call POpen with multiple files, forking and
running multiple programs, writing to each of these child processes
through a different pipe ?
Regards,
Adriaan van Os
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