Why Should You Retire the C `rand()` Function?

Dangers of Using rand(): Why the C Random Library Should Be Retired

Despite the widespread use of srand() to set a seed, the usage of rand() is strongly discouraged. What lies behind this disapproval?

Pseudorandom Number Generator Limitations

Rand is essentially a pseudorandom number generator. In other words, it relies on a seed value to produce a deterministic sequence. While this is suitable for certain applications, it falls short in scenarios requiring high security. Unlike true random generators, pseudorandom generators, including rand, can be predicted and exploited, rendering them unsuitable for sensitive operations.

C Random Library's Drawbacks

Beyond the limitations of pseudorandom generators, the C random library exhibits intrinsic shortcomings:

• Global State: Rand relies on a global state modified by srand(). This hampers multitasking and simultaneous utilization of multiple random engines.
• Lack of Distribution Engine: Rand generates numbers in a specific range [0, RAND_MAX]. However, for practical applications, random numbers within custom ranges are often required. Naive attempts to achieve this using rand() % [targetRange] can lead to non-uniform distribution, especially if RAND_MAX is not a multiple of the target range.
• Implementation Issues: The quality of rand's implementation varies among different systems. It has been subject to criticism regarding its efficiency and reliability.

Modern C Alternatives

In modern C , the library provides superior alternatives to the C random library:

• Multiple Random Engines: The library offers a variety of random engines, each with unique characteristics. This enables the simultaneous use of multiple random engines and facilitates multitasking.
• Distribution Classes: The library includes well-defined distribution classes for integer and floating-point types. These classes allow for the generation of random numbers within custom ranges with uniform distribution.
• High-Quality Implementation: The library has been designed and implemented with high standards, ensuring reliability and efficiency across different systems.

Therefore, while pseudorandom generators may suffice for certain tasks, the C random library's limitations and the availability of superior alternatives in modern C make the continued use of rand() obsolete. For reliable and secure random number generation, it is highly recommended to embrace the capabilities of the library.

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