My computer thinks Signed Int is less than -1?

#include 
int main(void)
{
 printf("%d", sizeof(signed int)> -1);
 return 0;
}

#include 
/* ... */
printf("%d", sizeof(signed int)> SIZE_MAX) ;

See the English answer> Why is (sizeof(int)> -1) false? 3
> Comparison operation on unsigned and signed integers 7

#include 
int main(void)
{
 printf("%d" , sizeof(signed int)> -1);
 return 0;
}

The result is 0(FALSE).
How could this be?
I am using 64-bit ubuntu linux, the result should be (4> -1)=> 1 => true.

sizeof(signed int ) Is of type size_t, which is an unsigned type. When you compare between signed and unsigned values ​​[and the type of the unsigned value is at least as large as the type of the signed value], before the comparison Convert a signed value to an unsigned value. This conversion makes -1 the largest possible value of an unsigned type. In other words, it’s just like you wrote

#include 
/* ... */
printf("%d", sizeof(signed int)> SIZE_MAX);

When you commit this You can make gcc warn when there is an error, but it is not even turned on by default-you need -Wextra or more specifically -Wsign-compare. (This warning will generate a lot of false positives, but I think it’s useful to open new code.)