Segmentation fault when accessing string array of struct

Question

Im currently running into an issue where I have to input words (strings) into a binary search tree and am doing so by putting words(strings) into string arrays, however when I try to put it into the first element, it is segmentation faulting.

Here is what I have:

node.h

typedef struct Node{
    char letter;
    int asiccValue;
    struct Node *left, *right;
    string words[99];
    int wordCount;
}Node;

tree.cpp

// This function creates new nodes as needed
Node *createNode(string word){
    // Assigns values
    struct Node *temp = (Node*)malloc(sizeof(Node));
    temp->letter = word[0];
    temp->asiccValue = (int)word[0];
    temp->left = NULL;
    temp->right = NULL;
    temp->words[0] = word;
    temp->wordCount = 1;
    return temp;
}

if string is actually std::string and this question is for the C++ programming language the answer will be radically different that it will be if string is a typedef and this is a C question. The crux would be under no circumstances should you malloc storage for std::string unless you're already an expert in C++ and would not need to ask this question. mallocing strings requires special handling (search keyterm: placement new) because malloc only provides storage. It does not call constructors, and an unconstructed string is a timebomb.. — user4581301
– user4581301, Commented Oct 13, 2020 at 3:34
Turns out vector is unnecessary. struct Node *temp = (Node*)malloc(sizeof(Node)); doesn't know how to construct the 99 strings in the word member of Node (see comment above). You can solve this with struct Node *temp = new Node; new allocates storage for and then constructs a Node. — user4581301
– user4581301, Commented Oct 13, 2020 at 3:46

Stephen Newell · Accepted Answer · 2020-10-13 04:53:26Z

1

malloc doesn't call constructors, meaning your string array isn't initialized. For any non-trivial type, you really want to avoid malloc unless you know what you're doing (see also: placement new).

Using new should fix your problem. Make sure you update existing code to use delete instead of free. Also, consider getting rid of new/delete entirely, and using make_unique and friends.

Node *createNode(string word){
    // Assigns values
    Node * temp = new Node;
    temp->letter = word[0];
    temp->asiccValue = (int)word[0];
    temp->left = NULL;
    temp->right = NULL;
    temp->words[0] = word;
    temp->wordCount = 1;
    return temp;
}

answered Oct 13, 2020 at 4:53

Stephen Newell

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1 Comment

Loki Astari Over a year ago

When using C++ you should avoid malloc as the memory is allocated in potentially different area than used by C++ programs that would normally use new. Mixxing dynamic memory allocation from different mechanism makes for potential issues.

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