I'm getting weird symbols in my output file instead of the appropriate letters

Question

I'm trying to print out a in order traversal of BST to a output file. However, I get weird symbols sometimes instead of the stdin.

I've tried allocating extra space for the char arr[] but it doesnt change anything.

EDIT: I changed up the code and tried splitting it into two parts. One, where a method assigns each node to a node array in inlevel order and returns that array. And two, a different array that writes the returned values contents to a file. This time though I'm getting 2 errors.

error: incompatible types when assigning to type ‘struct bstNode *’ from type ‘bstNode’ error: incompatible types when assigning to type ‘struct bstNode *’ from type ‘bstNode’

void traverseTree(bstNode *root){
        FILE *file;
        file = fopen("newFile", "w");
        char *arr;
        arr = (char*)malloc(10000 * sizeof(char));
        if(root == NULL)
                return;

        traverseTree(root->left);
        fgets(arr, 100, stdin);
        fprintf(file, arr);
        traverseTree(root->right);

}

New code below

bstNode* traverseTree(bstNode *root, int i){

        bstNode *arr[100];
        if(root == NULL)
                return;

        traverseTree(root->left, i);

        arr[i] = root;
        ++i;
        traverseTree(root->right, i);

 return *arr;
}

void writeToFile(bstNode *root, char *outputFileName){
        FILE *file;
        file = fopen("newFile", "w");
        bstNode *arr = traverseTree(root, 0);
        int i = 0;
        root = arr[i];
        while(root!= NULL){
        fprintf(file, root->data);
        ++i;
        root = arr[i];
        }

}

You have a recursive function that tries to open the same file every time its called. It makes no sense. — Tom Karzes, Jun 24 '19 at 01:14
You might be more clear about what the error looks like. In any case, you have a memory leak for not `free`-ing the `malloc`-ed array again. Far better is using an array with local storage duration: `char arr[10000];`, that one cleans up automatically. If you want to further improve: have the array just once, either as static variable or by setting it up in a non-recursive wrapper function and passing it to the recursive worker function as argument. — Aconcagua, Jun 24 '19 at 01:18
And if using `malloc`: You should *always* check the result for being `NULL`, otherwise you risk undefined behaviour (possibly resulting in crash). — Aconcagua, Jun 24 '19 at 01:19
[You should not cast the return value for malloc](https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) — Ed Heal, Jun 24 '19 at 01:25

Ed Heal · Answer 1 · 2019-06-24T05:48:25.997

Apart from the following

Opening the same file repeatedly
Not checking the return values from fopen and malloc
Not requiring the cast from malloc
Not checking the return value from fgets

The following line

fprintf(file, arr);

has a problem is arr has a % symbol in it (as this is for formatting - see the manual page)

Use the following

fprintf(file, "%s", arr);

instead.

EDIT

After your edit, another problem:

return *arr;

This is returning data that is on the stack - this will go out of scope.

Also still got the same problem with fprintf - please read the manual page for this

I'm getting weird symbols in my output file instead of the appropriate letters

1 Answers1