CODEWITHSUNDEEP
cstringpointers
glod
glod

Reputation: 1

How to access data given pointer?

I'm trying to learn C and having trouble accessing the data from a pointer of the data.

I have the example code:

// character array for string
char mystring[] = "Hello";

// store mystring's pointer
int p = *mystring;

printf("String to pointer is %d\n":, p);
>> String to pointer is: 1819043144

// trying to access data from pointer p
printf("%s",&p);
>> H

Why does this just "H" just get printed when I try and access the data from pointer p using the & operator?

Upvotes: 0

Views: 2135

Answers (1)

Barmar
Barmar

Reputation: 780818

The expression &p has nothing to do with mystring. p is an integer variable, and &p is the address of that variable.

int p = *mystring;

is equivalent to:

int p;
p = *mystring;

*mystring is the first element of the mystring array, which is the character 'H'. So this is equivalent to:

int p = 'H';

Your variable initialization is simply making a copy of the first character of mystring and putting that in p. It also converts it from a char to int.

When you try to print p using %s format, you're causing undefined behavior, because %s requires the corresponding argument to be a pointer to a null-terminated string, and you've given it a pointer to an int.

Compare your code with this:

int *p = mystring;
printf("%s", p);

This is closer to correct, because now p is a pointer, and it does point to the string. It's not a copy of anything. But it's still incorrect because the argument for %s must be char *, not int *. So you need to convert it:

printf("%s", (char *)p);

But the most proper way to do it is the declare p as the correct pointer type in the first place:

char *p = mystring;
printf("%s", p);

Upvotes: 3

Related Questions