there's no error or warning for redefining a same global variable

[realmz]

there's no error or warning when redefine a global varialbe (int a).

attached the test project.

# cat main.c

#include "MK64F12.h"

static int i = 0;

int a;
int a;

int main(void)
{

    /* Write your code here */

    /* This for loop should be replaced. By default this loop allows a single stepping. */
    for (;;) {
        i++;
    }
    /* Never leave main */
    return 0;
}

[David Brown (davidbrown)]

"int a;" is a "tentative definition You can have as many "tentative definitions" of an identifier as you want in a file. If no full defintion (such as with an initialiser "int a = 1;") or extern declaration is made for the identifier, then the compiler treats it as a definition.

So "int a; int a;" at file scope is just the same as "int a;" - it is fine to declare "a" twice.

But you'll get an error for "int a = 1; int a = 2;" because that would be two conflicting definitions.

If you want, you can use the warning flag "-Wredundant-decls" to give a warning on "int a; int a;" for redundant declarations. Personally, I use that flag - I would not intentionally declare "a" twice like this and so the flag might spot a typo or other mistake in my code.

[realmz (realmz6)]

Thanks for the explanation. The the warning flag "-Wredundant-decls" works.