Why Does My C Code Enter an Infinite Loop Despite a Seemingly Harmless Assignment?

Infinite Output Loop in C

In the provided C code, an unexpected endless loop occurs, printing a continuous series of numbers ("0, 1, 2, 3, 4, 5, ...") instead of the expected "0, 1, 2, 3".

Closer examination reveals that the culprit is the seemingly harmless assignment statement "delta = mc[di]" within the loop. This assignment triggers undefined behavior because it accesses the mc array out of bounds on the last iteration (i.e., "di = 4").

Under aggressive loop optimizations, the compiler may assume the absence of undefined behavior. As a result, it optimizes the loop by eliminating the di < 4 check, leading to continuous loop execution.

To ensure correct behavior, it is crucial to avoid undefined behavior, even within optimized code. In this case, the solution is to ensure that mc is accessed within bounds within the loop.

An alternative approach is to use the -fno-aggressive-loop-optimizations flag in gcc to disable aggressive loop optimizations. This flag forces the compiler to retain the di < 4 check and prevent the undefined behavior that leads to the infinite loop.

By comprehending the potential consequences of undefined behavior and taking appropriate measures to avoid it, programmers can ensure the reliability and correctness of their C code.

The above is the detailed content of Why Does My C Code Enter an Infinite Loop Despite a Seemingly Harmless Assignment?. For more information, please follow other related articles on the PHP Chinese website!