diffculty in entering strings in C using pointer

Question

The following program works in gcc but on giving the value of T = 6, this program continues and does not end on asking for input strings. Any help guys if you recognise whats wrong with this program?

int main()
{ int T,i,j;
  char *strings[T];
  printf("Enter the Number of Strings to Reverse : \n");

  scanf("%d ",&T);

  for(i=0;i<T;i++)
   { strings[i] = (char *)malloc(100*sizeof(char));
     scanf("%s\n",strings[i]);
   }
  for(i=0;i<T;i++)
   {printf(" The String %d is : %s\n",i+1,strings[i]);
  }
return 0;
}

T is uninitialized when you are creating your pointer array strings — Andreas Fester
– Andreas Fester, Commented Mar 5, 2014 at 18:45
@Andreas got it, but the array is 0 length (T would be initialized to 0), right? — John Yost
– John Yost, Commented Mar 5, 2014 at 18:48
But then strings is already allocated. Read stackoverflow.com/questions/14049777/… — Andreas Fester
– Andreas Fester, Commented Mar 5, 2014 at 18:52
@JohnYost local variables cannot be counted on to be initialized implicitly, so no, T would not (reliably) be initialized to 0. — mah
– mah, Commented Mar 5, 2014 at 18:52

Jeshen · Accepted Answer · 2017-05-20 20:08:05Z

2

T is not initialised (Remember in C++, local scope variables are not automatically initialised) :

int T= 6;

answered May 20, 2017 at 20:08

Jeshen

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Comments

abligh · Accepted Answer · 2014-03-05 19:11:51Z

1

T is not initialized inside main() therefore has an undefined value.

char *strings[T] creates an array of char * pointers of an undefined length.

Fix this using:

int T=6;

Or, given T is in fact constant:

const int T=6

or perhaps better

#define T 6

Feel free to use a more mnemonic name than T.

answered Mar 5, 2014 at 19:11

abligh

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4 Comments

user1463736 Over a year ago

but T value will be given by user when program executes.

Stefan Marinov Over a year ago

@user1463736, yes, but then the array of pointers is already allocated in memory!

user1463736 Over a year ago

@smarinov ok got it now. Thanks everyone for the help !

abligh Over a year ago

You could move the declaration of strings after T has been read. However, you are relying on (I believe) a gnu extension for that to work. A more common way would be to dynamically allocate a data structure of size T * sizeof (char *) using malloc().

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