Question

I recently came up with a question. Let’s say we have:

void test(int32_t b){
    printf("value is %d", b);
}

int main(){
    uint32_t a = 43;
    test(a);  
   return 0;
}

What happens when you pass a unsigned variable to a signed parameter? How does the copy of the value work, and how does the cast work?

Can someone explain it to me in detail?

Thanks

Answer 1

If the value is small enough, it is simply assigned. Otherwise it is assigned in an implementation-defined fashion. Typically this means it will “wrap around”.

6.3.1.3-1

When a value with integer type is converted to another integer type
other than _Bool, if the value can be represented by the new type, it
is unchanged.

Otherwise, if the new type is unsigned, the value is converted by
repeatedly adding or subtracting one more than the maximum value that
can be represented in the new type until the value is in the range of
the new type.

Otherwise, the new type is signed and the value cannot be represented
in it; either the result is implementation-defined or an
implementation-defined signal is raised.