gp_read_str

[Dirk Laurie <dirk.laurie@gmail.com>]

I'm programming in library mode, and have some GEN's around that
never were assigned to anything in a `gp_read_str` call.  I now want
to make such a call involving some of these GEN's, and find it hard
to get `gp_read_str` to see those GEN's. In the following minimal
example, I'm trying and failing to assign an expression to variable `b`.

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#include <pari/pari.h>

int main() {
   pari_init(1000000,0);
   GEN x = pol_x[fetch_user_var("x")];
   pol_x[fetch_user_var("b")] = gaddsg(1, x);
   pariprintf("%Z\n",pol_x[fetch_user_var("b")]);  // prints x+1
   pariprintf("%Z\n",gp_read_str("b+10"));  // prints b+10, not x+11
}
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