Code after function fails to execute - c++

Question

I am trying to write a program to simulate Huffman encoding and decoding. In order to do so, I needed to serialize a binary tree in a text file, so that I could read it again later and reconstruct the tree (when decoding the huffman file).

However, after my function (readBinaryTree) that reads the file (which is recursive), the program just stops executing. I've never seen this before.

Here's the code:

if (!decode) {
    .
    .
    .
    //alot of stuff here
    .
    .
    .
 }


else if (decode) {
    std::ifstream keyFile("hufftreekey.txt");

    Node* HuffTree = NULL;

     std::cout << "PRE!" << std::endl;

    readBinaryTree(HuffTree, keyFile);  //THIS FUNCTION EXECUTES, BUT NOTHING AFTER IT DOES

     std::cout << "POST!" << std::endl;


    std::map<char, std::string> codes = buildCodes(HuffTree);

    std::ofstream outFile;
    outFile.open ("mobydick_decoded.txt.huff");

    char c;
    std::ifstream input( argv[ 1 ] );
    while (input >> std::noskipws >> c) {
        if (codes.find(c) != codes.end()) { 
            std::string huffcode = codes[c];
            outFile << huffcode;
        }
        else{
            std::cout << "ERROR!" << std::endl;
        }

    }
    outFile.close();

}

Output in terminal is "PRE!", but it never prints "POST!". I don't get any error message, no exceptions are thrown, it just never prints, and nothing after the function is called is executed.

This is the function:

 void readBinaryTree(Node* root, std::ifstream &fin){
 std::string s_val;
 char val;
 std::getline(fin, s_val);
 val = s_val[0];
 if(val == '#')
     return;
 else if(val == '_') {
    root = new Node();
    if (root == NULL) {
        std::cout << "MEMORY ALLOC FAILURE!" << std::endl;
     }
    root->content = '_';
    readBinaryTree(root->leftChild, fin);
    readBinaryTree(root->rightChild, fin);

 }
 else {
     root = new Node();
     if (root == NULL) {
        std::cout << "MEMORY ALLOC FAILURE!" << std::endl;
     }
     root->content = val;
     readBinaryTree(root->leftChild, fin);
     readBinaryTree(root->rightChild, fin);
 }

}

This is not an infinite loop problem, the program finishes but it just seems to skip everything after the readBinaryTree function is called

Answer 1

You're not building a binary tree. You're leaking memory like a sieve leaks rain-water, then executing undefined behavior to add insult to injury.

Change this:

void readBinaryTree(Node* root, std::ifstream &fin)

to this:

void readBinaryTree(Node*& root, std::ifstream &fin)

// see addition here ====^

Try passing that pointer by reference (or address) and see what happens.

Answer 2

In C++, if new fails, it will NOT made the assigned pointer NULL. It will throw a std::bad_alloc exception. My guess is that root = new Node(); failed and an exception was raised but no catch was found by C++(Recall try{...}Catch{...} in C++ for exception handling). According to C++ standard, all uncaught exception will cause the program terminates immediately. Thus "PRE!" was printed but "POST!" was not. If you really want to use if(ROOT == NULL) to check whether dynamic memory allocation is successful, please use placement new like:

root = new (nothrow) node();

nothrow descriptor ensures that new will NOT throw an exception and will always return NULL if it fails.

I hope my explanation helps.