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(C++) std::rand

std::rand draws a random positive integer from zero to RAND_MAX. RAND_MAX is a #defined in cstdlib.h.

std::rand is defined in the header file cstdlib.h.

std::_lrand is like std::rand, except it returns random numbers in a larger range. Check out the Boost C++ library for other random number generators.

Examples

• std::rand example 1: drawing 10 random numbers
• std::rand example 2: std::rand draws same numbers after same seed
• GetRandomUniform: get a broken random number from zero to one
• GetRandomNormal: Get a random number from a normal distribution

Advice

• Prefer a random number class for a particular distribution over direct use of std::rand [1]
• Avoid using std::rand [2]
• Not all systems deliver a good std::rand [3]

Note when using multithreading

As std::srand and std::rand use a global/static variable and therefore is not suitable for multithreading. The Boost C++ library has other random number generators that do support multithreading.

External links

• Cplusplus.com page about std::rand

References

1. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. 40.8[15]: 'Prefer a random number class for a particular distribution over direct use of rand()'
2. Stephan T. Lavavej. 'rand() Considered Harmful'. 2013. GoingNative 2013
3. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. 40.7.4: 'Producing a random number generator isn't easy, and unfortunately not all systems deliver a good rand()'

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.