stack smashing detected by valgrind

Question

a stack smashing is detected in my main function in a c++ code... here is the body of main:

int main()
{
    long int acn;
    char dot[15];
    float open_balance=1;
    char k;
    int total_account=0;
    int c;
    static int ac=10000;
    TRANSACTION trn;
    support sprt;
    do{

        cout<<"\n1.New account\n2. Transaction\n3. Exit\n\nEnter choice:"; 
        cin>>k;
        switch(k) { 
            case '1':

                ac+=1;
                time_t rawtime;
                time(&rawtime);
                strcpy(dot,ctime(&rawtime));
                do{
                    if(open_balance<=0)
                        cout<<"Opening BALANCE can not be less than zero";
                    cout<<"\nEnter the opening balance :";
                    cin>>open_balance;
                }while(open_balance<=0);
                bln[total_account].get_data(ac,open_balance,dot);
                ++total_account;
                break;
            case '2':
                trn.trans(total_account);
                break;
            case '3': break;
            default :
                      cout<<"\nWrong choice!!";
        }
    }while(k!='3');
    cout<<"Thank you";
    return(0);
}

When i run the code through valgrind it also finds the stack smashing but can't find any memory leak. valgrind report:

1.New account 2. Transaction 3. Exit

Enter choice:3 * stack smashing detected *: ./a.out terminated Thank you==9813==

==9813== HEAP SUMMARY:

==9813== in use at exit: 0 bytes in 0 blocks

==9813== total heap usage: 10 allocs, 10 frees, 954 bytes allocated

==9813==

==9813== All heap blocks were freed -- no leaks are possible

==9813==

==9813== For counts of detected and suppressed errors, rerun with: -v

==9813== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0) Aborted (core dumped)

Where am i going wrong?

Answer 1

it's the line strcpy(dot,ctime(&rawtime)); which causes the stack smeshing.
function ctime returns a string alike "Wed Jun 30 21:49:08 1993\n", its length is more than 15 bytes, and you need more bytes to store the result of ctime.
strcpy does not check the margin of target memory, so it is considered dangerous, alternative strncpy is suggested instead. And, if your program runs more than one thread, ctime_r is preferred.