Typcast a null pointer to char*

Question

Suppose I have a char* elem that is supposed to hold a char**, such that elem[0] = char**, elem[1...m]= <more chars>. Is there a way I can put a null ptr within char* elem? When I try to set elem = NULL, it gives me a type error because NULL is an int.

Any help would be greatly appreciated!

Answer 1

If you are looking for a binary 0, try '\0'
That is null termination at the end of a string (char *)

Answer 2

If you have a plain char* foo variable then foo[0] will be of type char so you'll have to set it to \0 (or 0).

Answer 3

char* points to a char, not char*. Unless your architecture has 8-bit addresses or your characters are way wider than 8-bit, you can't possibly cram pointer into character.

Answer 4

The problem is not NULL vs. 0, they are the same and mean null-pointer which is a different concept than arithmetic 0 or binary 0. Your problem is most likely with the definition of your array.

String case (pointer to char):

char *s;
s = malloc(10 * sizeof(char));
s[0] = 'H';      /* set char */
s[1] = NULL;     /* not ok */
s[2] = '\0';     /* binary 0, end of string marker */

Pointer of pointer to char:

char **x;
x = malloc(10 * sizeof(char *));
x[0] = "Hello";  /* let it point to string */
x[1] = NULL;     /* let it point to nowhere */
x[2] = 0;        /* same thing as above */
x[3] = '\0';     /* bad, expects pointer to char not char */

Answer 5

I think you got the pointers mixed up.

char* - string
char ** - address of that string or an array of strings depending on your data
char *** - address of an array of strings.

Try re-reading your assignment maybe you got something wrong.

LE: And what Jeromi mentioned in his comment works.

typedef struct{

char** some_data

}info;

char* info;

If you want some char** to be NULL as some point just initialize your info->some_data to NULL when you allocate memory.