In C, consider missing arguments to printf: what will actually be printed (conceptually) by this code using bit shifts?
#include
int main()
{
printf("%d >> %d %d >> %d
", 4 >> 1, 8 >> 1);
return 0;
}
Note: The format string has four %d placeholders but only two arguments.
-
A4 1 8 1
-
B4 >> 1 8 >> 1
-
C2 >> 4 Garbage value >> Garbage value
-
D2 4
-
ENone of the above
Answer
Correct Answer: 2 >> 4 Garbage value >> Garbage value
Explanation
Introduction / Context:This question assesses understanding of printf formatting and undefined behavior when the number of conversion specifiers does not match the number of provided arguments. It also includes simple right-shift operations 4 >> 1 and 8 >> 1.
Given Data / Assumptions:
- Two arguments are supplied for four %d placeholders.
- 4 >> 1 equals 2; 8 >> 1 equals 4 for typical two’s complement integers.
- Accessing additional %d values with no corresponding arguments yields undefined behavior.
Concept / Approach:printf reads arguments from the stack/variadic argument list according to the format string. Missing arguments mean printf will fetch whatever bits happen to be present, leading to unpredictable “garbage” values for the third and fourth %d.
Step-by-Step Solution:First %d prints 4 >> 1 = 2.Literal text " >> " appears.Second %d prints 8 >> 1 = 4.Remaining two %d consume unspecified memory → unpredictable integers.
Verification / Alternative check:If the call were corrected to printf("%d >> %d %d >> %d", 4 >> 1, 1, 8 >> 1, 1), the output would be 2 >> 1 4 >> 1. As written, results beyond the first two are undefined.
Why Other Options Are Wrong:Literal or fully defined outputs ignore the argument mismatch.“2 4” omits the format text and still ignores missing arguments.
Common Pitfalls:Assuming printf quietly fills zeros; forgetting that varargs require a one-to-one match with conversion specifiers.
Final Answer:2 >> 4 Garbage value >> Garbage value