Preprocessor definitions not working in C - c

Question

I've been frantically trying to get this following code to work. The preprocessor definitions WIDR and LIDR aren't working and it's giving me the compile error:
projects/elcain.c: In function ‘main’:
projects/elcain.c:17:6: error: ‘WIDR’ undeclared (first use in this function)
if ( WIDR ) {
^
projects/elcain.c:17:6: note: each undeclared identifier is reported only once for each function it appears in
projects/elcain.c:19:13: error: ‘LIDR’ undeclared (first use in this function)
} else if ( LIDR ) {
I don't really have experience with preprocessor macros, or the preprocessor in general, so go easy on me.
Here's the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef _WIN32
#define WIDR 1
#elif defined _linux_
#define LIDR 1
#endif
int main () {
char* directory = (char*) malloc (1);
if ( WIDR ) {
strcpy(directory, "C:\\TEMP\\");
} else if ( LIDR ) {
strcpy(directory, "~/.temp/");
} else {
*directory = 0x00;
}
printf("%s\n", directory);
return 0;
}

Answer 1

You probably simply want this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main () {
#ifdef _WIN32
char directory[] = "C:\\TEMP\\";
#elif defined _linux_
char directory[] = "~/.temp/";
#else
#error Neither _WIN32 nor _linux_ are defined
#endif
printf("%s\n", directory);
return 0;
}

Answer 2

What you are looking for is something like this:
#include <stdlib.h>
#if defined unix || \
defined __unix || \
defined __unix__ || \
defined __linux__ || \
defined __FreeBSD__ || \
defined __CYGWIN__ || \
(defined __APPLE__ && defined __MACH__)
static const char TMP_DIR[] = "~/.temp/";
#elif defined WIN32 || \
defined _WIN32 || \
defined __WIN32
static const char TMP_DIR[] = "C:\\TEMP\\";
#else
#error "Platform not supported"
#endif
int
main(void)
{
printf("%s\n", TMP_DIR);
return EXIT_SUCCESS;
}

Answer 3

In fact both WIDR and LIDR are conditional compilation directives. In other words they exist at compilation time only.
Change your code like this:
#ifdef WIDR
strcpy(directory, "C:\\TEMP\\");
#elif defined LDIR
strcpy(directory, "~/.temp/");
#else
*directory = 0x00;
#endif
then compilation errors will gone