Array of Strings in C

A string in C is an array of characters treated as a single unit. For example:

           char str[6] =”hello”;

i.e. a string variable can store one string. If you need to handle array of strings, what is the solution?

You may use 2D array of characters to handle list of strings like 2D array. For example, you want to store month names of a year i.e. list of 12 months with max length 9 character(“September”). So the declaration will be:

                                                      

            char months [12] [10];

Where, 1^st subscript defines how many strings and 2^nd subscript defines how many characters in a string. 

You can initialize the 2D string following way:

char months[12][10]={ “January”, “February”, “March”, “April”, “May”, “June”, “July”,   

                                  “August”, “September”, “October”, “November”, “December”}

And this list of string can be represented in memory as follows:

J	a	n	u	a	r	y	‘\0’
F	e	b	r	u	a	r	y	‘\0’
M	a	r	c	h	‘\0’
A	p	r	i	l	‘\0’
M	a	y	‘\0’
J	u	n	e	‘\0’
J	u	l	y	‘\0’
A	u	g	u	s	t	‘\0’
S	e	p	t	e	m	b	e	r	‘\0’
O	c	t	o	b	e	r	‘\0’
N	o	v	e	m	b	e	r	‘\0’
D	e	c	e	m	b	e	r	‘\0’

If we look at the memory representation table, total 120 bytes used to store this list of strings. But if we count the total characters in a list, only 86 bytes requires to store the list. So 34 (120-86) bytes wastage.

That’s why most efficient way of storing list of strings is array of pointers to strings and declared as follows:

char *months [12] = { “January”, “February”, “March”, “April”, “May”, “June”, “July”,  

                                 “August”, “September”, “October”, “November”, “December”}

And the memory representation will be:

J	a	n	u	a	r	y	‘\0’
F	e	b	r	u	a	r	y	‘\0’
M	a	r	c	h	‘\0’
A	p	r	i	l	‘\0’
M	a	y	‘\0’
J	u	n	e	‘\0’
J	u	l	y	‘\0’
A	u	g	u	s	t	‘\0’
S	e	p	t	e	m	b	e	r	‘\0’
O	c	t	o	b	e	r	‘\0’
N	o	v	e	m	b	e	r	‘\0’
D	e	c	e	m	b	e	r	‘\0’

Now 86 bytes required to store the list, so no memory wastage. But there is one limitation in array of pointers to strings. We cannot receive strings from keyboard using scanf() function. So the following code segment will not work during execution:

int main()

{

    char *names[5];

    int count;

    for(count=0;count<=5;count++)

        scanf("%s",names[count]);            

    return 0;

}

We can solve this problem by allocating space using malloc() following way:

int main()
{    
      char *names[5], str[20];    
      int count;    
      for(count=0;count<=5;count++)    
      {       
            scanf("%s",str);
            names[count] = (char*)malloc(sizeof(str));
            strcpy(names[count],str);
       }      
       for(count=0;count<=5;count++)       
           printf("%s\n",names[count]);        
       return 0;
}