C-在数组混乱中存储结构

Question

Good morning, I am currently working on an app for Pebble Smartwatch which uses standard C, a language I just started with.

I have a function that adds a Money Transaction to an array. I have defined Transaction like this:

struct Transaction {
    char * title;
    char * amount;
    char * date;
    char * text;
} txnsArray[20];

whenever I receive a transaction it is added to the txnsArray using this function:

void addTransaction(DictionaryIterator * txnIter){
    Tuple *txnTitle_Tuple = dict_find(txnIter, TRANSACTION_TITLE);
    Tuple *txnAmount_Tuple = dict_find(txnIter, TRANSACTION_AMOUNT);
    Tuple *txnText_Tuple = dict_find(txnIter, TRANSACTION_TEXT);


    txnsArray[transOverview.txnCounter].title = txnTitle_Tuple->value->cstring;
    txnsArray[transOverview.txnCounter].amount = txnAmount_Tuple ->value->cstring;
    txnsArray[transOverview.txnCounter].text = txnText_Tuple->value->cstring;

    transOverview.txnCounter++;

}

Now when I check this array it does add entries as it is supposed to, however the last transaction I add applies to all entries.

Say I first add a transaction wight he amount 2.5 € and then another one with 4.0€ then both entries will have 4.0€.

What am I doing wrong? Help is much appreciated. :)

Answer 1

It looks like the dict_find function does not allocate memory for value->cstring but uses the same buffer for each call. So the structs in your array end up with pointers to the same memory, and if dict_find modifies it, it modifies all array entries.