CODEWITHSUNDEEP
cmemory-managementrealloc
lian
lian

Reputation: 543

Error during memory reallocation inside a function

I wrote a function to append pointer to an object to array, but realloc can't properly reallocate memory when it's called from a nested function. However, when I'm reallocating memory from function, where object has been previously allocated, everything is alright

Here is a simplified example of my code:

#include <stdlib.h>

typedef struct Node
{
    char ch;
    int freq;
    struct Node *left, *right;

} Node;

Node *newNode(char ch, int freq, Node *left, Node *right)
{
    Node *node = (Node *)malloc(sizeof(Node));
    node->ch = ch;
    node->freq = freq;
    node->left = left;
    node->right = right;

    return node;
};

void pushNode(Node **nodes, Node *node, int *nodesCount)
{
    nodes = (Node **)realloc(nodes, ++(*nodesCount) * sizeof(Node *)); // error
    nodes[*nodesCount - 1] = node;
}

int main()
{
    int nodesCount = 0;
    Node **nodes = (Node **)calloc(0, sizeof(Node *));

    Node *node = newNode('\0', 0, NULL, NULL);
    pushNode(nodes, node, &nodesCount);

    for (int i = 0; i < 256; i++)
    {
        node = newNode((char)i, i, NULL, NULL);
        // pushNode(nodes, node, &nodesCount);
        nodes = (Node **)realloc(nodes, ++nodesCount * sizeof(Node *)); // no error
        nodes[nodesCount - 1] = node;
    }

    free(nodes);

    return 0;
}

Running the code above causes the following error:

test(94309,0x1ec9f2500) malloc: *** error for object 0x60000020c020: pointer being realloc'd was not allocated
test(94309,0x1ec9f2500) malloc: *** set a breakpoint in malloc_error_break to debug

Upvotes: 0

Views: 108

Answers (1)

Mathieu
Mathieu

Reputation: 9659

Your error comes from nodes that is local to pushNode function, you should have something like:

void pushNode(Node ***nodes, Node *node, int *nodesCount)
{
    Node **newNodes;
    newNodes = (Node **)realloc(*nodes, ++(*nodesCount) * sizeof(Node *));
    /* check newNodes */
    *nodes = newNodes
    (*nodes)[*nodesCount - 1] = node;
}

Upvotes: 1

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