My code is:
#include <stdio.h>
#include <string.h>
void main()
{
char string[10];
int A = -73;
unsigned int B = 31337;
strcpy(string, "sample");
// printing with different formats
printf("[A] Dec: %d, Hex: %x, Unsigned: %u\n", A,A,A);
printf("[B] Dec: %d, Hex: %x, Unsigned: %u\n", B,B,B);
printf("[field width on B] 3: '%3u', 10: '%10u', '%08u'\n", B,B,B);
// Example of unary address operator (dereferencing) and a %x
// format string
printf("variable A is at address: %08x\n", &A);
I am using the terminal in linux mint to compile, and when I try to compile using gcc I get the following error message:
basicStringFormatting.c: In function ‘main’:
basicStringFormatting.c:18:2: warning: format ‘%x’ expects argument
of type ‘unsigned int’, but argument 2 has type ‘int *’ [-Wformat=]
printf("variable A is at address: %08x\n", &A);
All I am trying to do is print the address in memory of the variable A.
Use the format specifier %p
:
printf("variable A is at address: %p\n", (void*)&A);
The standard requires that the argument is of type void*
for %p
specifier. Since, printf
is a variadic function, there's no implicit conversion to void *
from T *
which would happen implicitly for any non-variadic functions in C. Hence, the cast is required. To quote the standard:
7.21.6 Formatted input/output functions (C11 draft)
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.
Whereas you are using %x
, which expects unsigned int
whereas &A
is of type int *
. You can read about format specifiers for printf from the manual. Format specifier mismatch in printf leads to undefined behaviour.