Show gcc's behavior regarding string literals and -Wformat-security.

strings.c

/*
 * Show gcc's behavior regarding string literals and -Wformat-security.
 *
 * gcc -Wformat -Wformat-security -Wall -Werror -o strings strings.c
 *
 * GPLv2+ Kees Cook <[email protected]>
 */
#include <stdio.h>

struct structure {
	int thing;
	const char *name;
};
struct cstructure {
	int thing;
	const char name[128];
};

int main(void)
{
	char array[] = "This is a char array\n";
	const char carray[] = "This is a const char array\n";
	const char cnarray[64] = "This is a sized const char array\n";
	char *ptr = "This is a char pointer\n";
	const char *cptr = "This is a const char pointer\n";
	const char const *ccptr = "This is a const char const pointer\n";
	struct structure instance[] = {
		[0] = { 1, "This is a structure\n" },
	};
	const struct structure cinstance[] = {
		[0] = { 1, "This is a const structure\n" },
	};
	struct cstructure instancec[] = {
		[0] = { 1, "This is a structure with const char\n" },
	};
	const struct cstructure cinstancec[] = {
		[0] = { 1, "This is a const structure with const char\n" },
	};

	/* These correctly do not warn. */
	printf("This is a literal char array\n"); // safe
	printf(carray);	// safe
	printf(cnarray); // safe

	/* These correctly warn. */
	printf(array); // unsafe
	printf(ptr); // unsafe
	printf(instance[0].name); // unsafe
	printf(instancec[0].name); // unsafe

	/* These should not warn. */
	printf(cptr); // should be safe
	printf(ccptr); // should be safe
	printf(cinstance[0].name); // should be safe
	printf(cinstancec[0].name); // should be safe

	return 0;
}