I accidentally used "%d" to print an unsigned integer using an online compiler. I thought errors would pop out, but my program can run successfully. It’s good that my codes are working, but I just don’t understand why.
#include <stdio.h>
int main() {
unsigned int x = 1
printf( "%d", x);
return 0;
}
>Solution :
The value of the "unsigned integer" was small enough that the MSB (most significant bit) was not set. If it were, printf() would have treated the value as a "negative signed integer" value.
int main() {
uint32_t x = 0x5;
uint32_t y = 0xC0000000;
printf( "%d %u %d\n", x, y, y );
return 0;
}
5 3221225472 -1073741824
You can see the difference.
With new-fangled compilers that "read into" printf format specifiers and match those with the datatypes of following parameters, it may be that the online compiler may-or-may-not have been able to report this type mismatch with a warning. This may be something you will want to look into.