Printing string from array prints wrong result

Question

Hey I was wondering if I could get some help on this. I have an array that was given to me like this:

char **indexArray;

And I was told to add to the array like this:

indexArray[recCount++]=root->data;

recCount isn't important, but essentially, when I do this, I tried this:

printf(indexArray[recCount]);
printf(root->data);

Yet for some reason, the output is this:

ðy
test

Anyone know why?

Edit: @MikeCAT My node setup is as follows:

    numNodes += 1;

    struct bNode *node = (bNode *) malloc(sizeof(bNode));
    node->data = data;
    node->left  = NULL;
    node->right = NULL;
    printf(node->data); #prints the data I want so this works just fine
    return node;
}

Then I do something along the lines of:

bNode root = makeNode("test")

then I do this:

indexArray[recCount++]=root->data;

Yet when I do this:

printf("%s", indexArray[0]);

I either get some random character, (null), or just a blank line.

MikeCAT · Accepted Answer · 2020-12-06 00:38:41Z

1

The expression recCount++ is add one to recCount and evaluated to the value of recCount before the addition.

Therefore, you should use indexArray[recCount-1] instead of indexArray[recCount] to get the assigned value after that.

Also

printf(indexArray[recCount]);
printf(root->data);

looks dangerous because it will interpret % in the data as format specifier and invoke undefined behavior because there are not data corresponding to the specifiers if it is included.

It should be

printf("%s", indexArray[recCount]);
printf("%s", root->data);

or

fputs(indexArray[recCount], stdout);
fputs(root->data, stdout);

answered Dec 6, 2020 at 0:38

MikeCAT

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2 Comments

efun Over a year ago

My node setup is as follows:

struct bNode *makeNode(char *data) {     numNodes += 1;      struct bNode *node = (bNode *) malloc(sizeof(bNode));     node->data = data;     node->left  = NULL;     node->right = NULL;     printf(node->data); #prints the data I want so this works just fine     return node; }

Then I do something along the lines of: bNode root = makeNode("test") then I do this: indexArray[recCount++]=root->data; Yet when I do this: printf("%s", indexArray[0]); I either get some random character, (null), or just a blank line.

efun Over a year ago

any ideas of how to fix this please?

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