Variable is correct, but test case does not execute-CodePudding

I wrote the following code:

#include <stdio.h>

int array[] = {23, 43, 12, 17, 204, 99, 16};
#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))

int main()
{
        int test = -1;

        if (test <= TOTAL_ELEMENTS)
        {
                printf("Hello, got here!\n");
        }
}

When I compile this code (with gcc main.c -Wall (no warnings!)), and run it, the printf fails to execute. I mean, test = -1, and that is definitely smaller than the size of the array (7 digits). Where is the bug?

CodePudding user response：

The bug was in the difference between unsigned and signed. Specifically, the defined variable TOTAL_ELEMENTS's type is unsigned int (sizeof returns unsigned because a size can never be negative). The test is comparing a signed int with an unsigned int. That fails because test is promoted to unsigned. -1 turned into unsigned becomes a large positive integer, thus making the if conditional return false.

If you compile with gcc main.c -Wall -Wextra it will warn.