Question

I need to implement a method that concatenates different characters into a char* without using any standard library (it’s part of the specifications). So, no strcat or strcopy. I can’t use strings neither.

Here’s what I tried to do (the chars are stored in a StringList I implemented myself, hence the “GetCell” method and the ->next pointer) :

  char* IntlFinder::ConcatenateSrc ( int nSource, long beginPosition )
        char* res = new char;
        Cell* cell = ComList.GetCell(beginPosition);
        for (long i = beginPosition; i <= (CountTab[nSource]); i++)
        {
            if (nSource == 0 || cell->elem.source == nSource)
            {
                res[i-beginPosition] = cell->elem.caractere;
            }
            cell = cell->next;
        }

        *res = '\0';
        return res;
    }

When I’m debugging, this looks great until I get to a certain char, and then it bugs for no reason (the cell it’s pointing to at that moment looks normal, with a valid adress).

Any thoughts on that?

—

EDIT: I tried to do this instead:

    for (long i = beginPosition; i <= (CountTab[nSource]-1); i++)
    {
        if (nSource == 0 || cell->elem.source == nSource)
        {
            *res = cell->elem.caractere;
            ++res = new char;
        }
        cell = cell->next;
    }

Which is supposed to increment the pointer and allocate memory (so I can add another value at the next iteration), and I don’t have any SIGSERV error anymore.
But when I return this pointer or the original value of the pointer, poiting to the first char, I get nothing (in the first case) or just the first character (in the second case).

I didn’t forget to add ‘\0’ at the end, but this still doesn’t make it a string.

Answer 1

Something like:

char * concat(char dest[], char src[])
{
   int i = 0, j = 0;
   while (dest[i]) ++i;
   while (src[j]) dest[i++] = src[j++];
   dest[i] = '\0';
   return dest;
}

Provided that dest is big enough to carry both itselt and src. Otherwise, this may cause unexpected results because of writing outside the bounds of array.

ADD

int main()
{
    char * buf = new char[1 << 30]; // allocate 2^30 = 1e9+ chars (very huge size)
    // you can use char buf[1 << 30];
    // which is faster and not needing to be released manually
    char tmp[] = "First portion";
    char tmp2[] = "Second porition";
    buf[0] = '\0'; // so that concat begins copying at 0
    concat(buf, tmp);
    // buf == "First portion"
    concat(buf, tmp2);
    // buf = "First portionSecond portion"

    ....
    // don't forget to release memory after you have finished
    delete[] buf;
    return 0;
}