Example pointer in C not working

Question

i'm new learning C, and learning pointer right now,i study from this website, but this code give me an error : pointer.c: In function ‘main’: pointer.c:6:5: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int *’ [-Wformat=] printf("Address: %d",&var); //Notice, the ampersand(&) before var.

i compile it with : gcc -o pointer pointer.c

/* Example to demonstrate use of reference operator in C programming. */
#include <stdio.h>
int main(){
int var = 5;
printf("Value: %d\n",var);
printf("Address: %d",&var);  //Notice, the ampersand(&) before var.
return 0;
}

http://www.programiz.com/c-programming/c-pointers

Use %p for printing pointer values. – Jean-Baptiste Yunès Feb 18 '16 at 10:58 — Jean-Baptiste Yunès, Feb 18 '16 at 10:58
Unrelated, but you should indent your code. – Jabberwocky Feb 18 '16 at 11:03 — Jabberwocky, Feb 18 '16 at 11:03
yes its working. :) thank you, – mas bro Feb 18 '16 at 11:07 — mas bro, Feb 18 '16 at 11:07

score 2 · Accepted Answer · answered Feb 18 '16 at 10:59

You're trying to print the address of var as if it was a signed integer, which it isn't. It's a pointer, and might have a different size than an integer.

Passing values of mismatching types to printf() invokes undefined behavior, which is why the compiler is issuing a friendly warning.

You should use %p to format it, and cast the value to (void *) to comply with the C standard:

printf("Address: %p\n", (void *) &var);

score 2 · Answer 2 · answered Feb 18 '16 at 11:01

2

Please use correct format specifiers for each data type. Addresses are specified by %p.

answered Feb 18 '16 at 11:01

jada12276

129
8

score 1 · Answer 3 · answered Feb 18 '16 at 10:59

It's better if you use %p to print a pointer. From the specification:

p The argument shall be a pointer to void. The value of the pointer is converted to a sequence of printing characters, in an implementation-defined manner.

Don't forget the cast: printf("Address: %p\n",(void*)&var);

Example pointer in C not working

3 Answers3