CODEWITHSUNDEEP
carrayspointersdynamic-memory-allocation
user6843746
user6843746

Reputation:

lvalue required as left operand of an assignment?

Here is my code:

void pwd(Fs_sim *files) {
    Node *curr_node = files->curr;
    Node **space = NULL;
    int i = 0;

    while (curr_node->parent != NULL) {
        space = realloc(space, sizeof(Node *) * (i + 1));
        *space + i = curr_node;
        i++;
        curr_node = curr_node->parent;
    }
    if (i == 0)
        printf("/\n");
    else {
        while (i > 0) {
            printf("/%s", (*space + i--)->name);
        }

        printf("\n");
    }
    free(space);

}

'space' is a pointer to an array that's being dynamically allocated. As each node being iterated through, I'd like to store a pointer to that node in the dynamically allocated array, and keep a count of how many elements there are. I get the error message:

error: lvalue required as left operand of an assignment

on the '*space + i = curr_node;' line.

I don't see what's wrong with it. Can someone clarify?

UPDATE:

I have changed the code and it now compiles, but I get segmentation fault when I run the executable. Here's my code:

void pwd(Fs_sim *files) {
    Node *curr_node = files->curr;
    Node **space = NULL;
    int i = 0;

    while (curr_node->parent != NULL) {
        space = realloc(space, sizeof(Node *) * (i + 1));
        *(space + i) = curr_node;
        i++;
        curr_node = curr_node->parent;
    }
    if (i == 0)
        printf("/\n");
    else {
        while (i >= 0) {
          printf("/%s", (*(space + (i-1)))->name);
          i--;
        }

        printf("\n");
    }
    free(space);

}

still can't find what's wrong with it.

Thanks ahead of time. Big noob to C here.

Upvotes: 0

Views: 84

Answers (2)

smac89
smac89

Reputation: 43138

The error I believe is here:

while (i >= 0) {
    printf("/%s", (*(space + (i-1)))->name);
    i--;
}

What happens when i is 0 and you try to do (*(space + (i-1)))->name);?

You get space + -1!

Upvotes: 1

Vincent T
Vincent T

Reputation: 185

Pre-update answer:

You appeared to have flipped it around, it should be curr_node = *space + i. It's because the variable whose value of an expression that you want to assign should be on the left, as you can't assign curr_node into a sum of two variables

It that isn't quite right for your purpose, you can also do *(space + i) = curr_node

Upvotes: 1

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