I've encountered a warning that I don't really understand. The warning is generated by comparing what I consider to be one unsigned with another unsigned.
Here is the source:
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
int main()
{
uint8_t *arr = malloc(8);
assert(arr);
/* fill arr[] with stuff */
if (arr[3] != (uint8_t)(~arr[2])) { // Warning is here
/* stuff */
}
return EXIT_SUCCESS;
}
Which I build using the following procedure:
user@linux:~ $ gcc -o test -Wall -Wextra test.c
test.c: In function ‘main’:
test.c:13:16: warning: comparison of promoted ~unsigned with unsigned [-Wsign-compare]
I'm using gcc version 4.7.2 20121109 (Red Hat 4.7.2-8)
How can I fix the above comparison?
I had the same problem and I worked around it by using an intermediate variable:
uint8_t check = ~arr[2];
if (arr[3] != check)
Yes I think its a bug. Read [Bug c/38341] Wrong warning comparison of promoted ~unsigned with unsigned and also Why, warning: comparison between signed and unsigned integer expressions?. This might help you.
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