Why is `rand()` Considered a Bad Practice in C and What are Better Alternatives?

Why Using 'rand()' is Considered Bad Practice

Despite the possibility of setting a seed with 'srand()', the utilization of 'rand()' is generally discouraged. This article delves into the reasons behind this notion and explores more suitable alternatives.

The Drawbacks of 'rand()'

'rand()' operates as a pseudorandom number generator, relying on a seed to generate a sequence. This implies that a predetermined seed consistently yields the same sequence. While this may be sufficient for certain applications, it poses challenges when security is paramount.

C Random Library Deficiencies

Beyond this fundamental limitation, the C random library (encompassing both 'rand()' and 'srand()') faces further setbacks:

• Global State: The library maintains a global state influenced by 'srand()'. This restricts the concurrent use of multiple random engines, complicating multithreaded scenarios.
• Lack of Distribution: 'rand()' yields numbers within a defined range ([0, RAND_MAX]), with each number having an equal probability of occurrence. However, many applications require random numbers within specific intervals. Naive approaches, such as 'rand() % 1018' for a range of [0, 1017], are flawed as they don't guarantee uniform distribution unless RAND_MAX is a perfect multiple of the desired interval.
• Quality of Implementation: The implementation of 'rand()' has inherent limitations, making it unreliable for several applications.

C Alternatives

Contemporary C developers should leverage the superior 'random' library, offering a range of well-defined random engines and distributions for both integer and floating-point data types. This library provides robust and versatile alternatives to the obsolete 'rand()' function.

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