Re: CurrentMemoryContext and MemoryContextStrdup

Thank you very much for your answer.
Well, you told me that pstrdup was not going to help me in the context of
my use case.
And that I would have to use MemoryContextStrdup.
And the truth is that this part costs me a bit, even though I have the
definitions of MemoryContextStrdup in the .c, since I can't find an example
of a source code that uses it, it's hard for me to apply things by
definition just.
By telling me: "Copying it into a different context would be the way to do
that", I understand better.
Now, as I understand it (I don't know if I'm right), what I would have to
do would be this:
1. I save the CurrentMemoryContext, for example as follows:
MemoryContext oldcontext = CurrentMemoryContext;
2. I make the call to SPI, which was what caused the context problem.
3. I copy my variable in a different context, for example as follows:
MemoryContext newcontext;
char * copy = MemoryContextStrdup (newcontext, data);
4. Then, at the end of my call to SPI, after SPI_finish () I would have in
the copy variable, the copy of the data variable, to use it as I want.
Is that so? I am correct at least to try to modify my program or is it
totally something else what should I do?
Best regards,
Yessica Brinkmann

El mar., 26 nov. 2019 a las 13:48, Tom Lane (<tgl(at)sss(dot)pgh(dot)pa(dot)us>) escribió:

> Yessica Brinkmann <yessica(dot)brinkmann(at)gmail(dot)com> writes:
> > Thank you very much for the reply!
> > Not really, I don't feel better informed because MemoryContextStrdup is
> not
> > even mentioned once in the README.
>
> The next thing to do would be to look at that function's header comment
> (find it in src/backend/utils/mmgr/mcxt.c):
>
> /*
> * MemoryContextStrdup
> * Like strdup(), but allocate from the specified context
> */
> char *
> MemoryContextStrdup(MemoryContext context, const char *string)
>
>
> As I recall your original problem, people were suggesting that
> you make a longer-lived copy of some transiently-allocated
> string. Copying it into a different context would be the
> way to do that, as I hope you now understand from the README
> discussion, and this function is the easiest way to do that.
>
> Or at least the second easiest; the very easiest is pstrdup,
> which is just
>
> char *
> pstrdup(const char *in)
> {
> return MemoryContextStrdup(CurrentMemoryContext, in);
> }
>
> but I don't remember whether the current context was a suitable
> target for your use-case.
>
> regards, tom lane
>