realloc() : Invalid pointer in C

Question

Net is a structure which contain

typedef struct net{
    int numele;
    struct net **e;
} net;

The following code raises the error:

realloc(): invalid pointer

The realloc is causing problems whenever it is accessed and gives the above error. I don't understand why. If you think there is no problem in this part of the code, let me know because the whole code is 800 line long so i don't think I can post it here.

void add(net *n, net *ne) {
    if(n->numele==0) {
        n->e = (net **)malloc(sizeof(net *));
        n->e[0] = ne;
        n->numele = 1;
    } else {
        n->e = (net **)realloc(n->e, (1 + n->numele)*sizeof(net *));
        n->e[n->numele] = ne;
        n->numele = n->numele + 1;
    }
}

The nets n and ne are already initialized somewhere else in the code, so you can assume that they will not be null.

[Please see this discussion on why not to cast the return value of `malloc()` and family in `C`.](http://stackoverflow.com/q/605845/2173917). — Sourav Ghosh, Mar 08 '17 at 06:46
You mind creating a [___MCVE___](http://stackoverflow.com/help/mcve)? — Sourav Ghosh, Mar 08 '17 at 06:47
@SouravGhosh - I learned a neat feature of comments the other day, if you enter the markup `[mcve]` is expands to [mcve]. — StoryTeller - Unslander Monica, Mar 08 '17 at 06:53
@StoryTeller Right, that's the way it is, also helps while suggesting [edit]. — Sourav Ghosh, Mar 08 '17 at 07:08
Posted code seems OK if rather inefficient (except return value of malloc/realloc is not checked). The problem is elsewhere. — n. m. could be an AI, Mar 08 '17 at 08:57
You'll need to provide a simple `main()` so that we can see how `n` and `ne` are initialized. Simply asserting that "somewhere else in the code" is all correct isn't very convincing. Please [edit] your question so that it has a [mcve] that anyone can reproduce. — Toby Speight, Mar 09 '17 at 16:33

score 0 · Answer 1 · answered Mar 08 '17 at 10:34

0

Code for realloc() seems to be OK. But if net *n is not initialized properly in first call of add(), ie numele != 0 && e != NULL. In such cases e might have some junk values and realloc() tries with invalid address. So that error can happen.

answered Mar 08 '17 at 10:34

jjm

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realloc() : Invalid pointer in C

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