How to loop through double pointers without knowing size. (C)

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How can I loop through this double pointer without knowing it's size.

char *arr[] = {"ant", "bat", "cat", "dog", "egg", "fly"}; 
char **ptr = arr; // Double pointer

I tried this but I get an error

while (*ptr){
   printf("%s\n",*ptr);
   ptr+=1;
}

I wan't something similar to this but with double pointers.

char *word = *ptr;
for (int i = 0; *(word + i) != '\0'; i++)
{
   printf("%c", *(word + i));
}
pointers c
1 Answers

The reason you can determine the end of a string with \0 is because when you assign one to a pointer a null byte is automatically placed at the end, note that the definition of string is a null terminated array of characters. You can mimic this behavior in an array of strings by adding a NULL element at the end:

char *arr[] = {"ant", "bat", "cat", "dog", "egg", "fly", NULL};
char **ptr = arr;  // Double pointer

while (*ptr) {
    printf("%s\n", *ptr);
    ptr += 1;
}

This is what is called a sentinel.

user_68659320
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