Thread: Strings

I am trying to create a dynamic string array in C++ that will read in words from a file. The length of the words and how many words will belong in the array is unknown.

In the class XYZ, there is the following var char *str[];

Code:

XYZ obj;
ifstream in;

.....
.....

while (!in.eof())
   in >> obj.str[i++]>> ws;

This isnt working. I know that char *tmp will let me store a word of any length (of course with the use of new) but if I want to make an array of words, I cant do it.

thanx

Well I was originally reading in the words and storing them into a linked list, but I thought that this might take up alot of memory because the file it is going to read has 1000's of words.

Then I have another question. I am not to sure which way is the proper way of using new and delete i.e to make sure I am releasing ALL the memory I am using. This is of great importance to me.

Code:

SomeClass::SomeFnct()
{
   FOO obj;

   obj.str = new char; //should this be here or in the loop

   infile.open("somefile.txt");   

   if (!infile())
  {
     cout << "unable to open file";
  else
 {

   while (!infile.eof())
   {
     // obj.str = new char;
      infile >> obj.str >> ws;
      makeLink(obj);//for the linked list
      delete obj.str; //would I need to release the memory here or at the end of the function
    } //while
  
      ..
      ..
      ..
  }//else

  infile.close();
   // delete obj.str;
}

Thank you to all that replies

use new and delete to work with dynamic memory for a given object and new [] and delete [] to work with dynamic memory for an array of objects. Routinely you allocate memory for a given object/array of objects just in the nick of time, you also routinely delete memory as soon as you are done with it. If you are using classes the allocation frequently occurs in the constructor and the release frequently occurs in the destructor.

If you are using an array of Cstyle strings, then you will basically have:

char array[#ofStrings][#sizeOfLongestString + 1];

memory for array can be allocated on the stack on loading the program into memory, or on the heap, during the program as needed. Unless all the strings are of the same size you will be "wasting" memory in each of the strings that are shorter than the longest, so there is often no way of getting around the wasting of memory concern. Generally, unless you know memory is likely to be a major issue with your program I'd use whichever you are most comfortable with: an array of C style strings, a list of C style strings, or a vector of STL strings, and disregard the concern for memory wasting---at least until you get to the advanced stage of your program writing careeer.