Using C-string gives Warning: “Address of stack memory associated with local variable returned”

Question

I am not a C programmer, so I am not that familiar with C-string but now I have to use a C library so here is a shortened version of my code to demonstrate my problem:

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Answer 1

When you return the matches array, what you are returning is the address of the first element. This is stored on the stack inside my_completion. Once you return from my_completion that memory is reclaimed and will (most likely) eventually be reused for something else, overwriting the values stored in matches - and yes, that may well be why your application doesn't work - if it isn't right now, it probably will be once you have fixed some other problems, or changed it a bit, or something else, because this is not one of those little warnings that you can safely ignore.

You can fix this in a few different ways. The most obvious is to simply use std::vector [or better yet std::vector] instead:

std::vector ReadLineImpl::my_completion ()
{
    std::vector strings;
    strings.push_back("add");
    return strings;
}

Edit: So, if the library requires a char ** as per the readline interface,then use this:

char** ReadLineImpl::my_completion ()
{
    char **matches = static_castmalloc(1 * sizeof(char *));
    matches[1] = "add";
    return matches;
}

Problem solved!