What's the Difference Between Indeterminate and Undefined Behavior in C and C?

Indeterminate vs. Undefined Behavior in C and C

In C and its precursor C, various levels of behavioral outcomes can arise from code, each with distinct implications for program execution.

Indeterminate Behavior

Indeterminate behavior occurs when the C or C standard does not specify a precise result for a particular code construction. The behavior is left undefined, and the compiler or runtime system is free to choose an arbitrary outcome. Assigning an uninitialized variable, for instance, results in an indeterminate value. This value could be anything and may vary across different compiler implementations or even the same compiler under different circumstances.

Undefined Behavior

Undefined behavior is a more severe situation where the behavior is not just unspecified but outright undefined. The program may exhibit unpredictable behavior, including memory corruption, program crashes, or incorrect execution. Examples of undefined behavior include accessing out-of-bounds array elements or using null pointers.

Distinction

Indeterminate behavior implies that the result is not specified by the standard, while undefined behavior indicates that the outcome is unpredictable and can lead to program failure or erroneous behavior. Indeterminate behavior is a subclass of undefined behavior, with undefined behavior being the most extreme case.

Classification in C Codes

The classification of indeterminate and undefined behavior is equally valid for C codes. The concepts and terminology are defined in the C standard and apply to both C and C programming languages.

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