29 Numerics library [numerics]

29.5 Random number generation [rand]

29.5.10 Low-quality random number generation [c.math.rand]

[Note 1: 
The header <cstdlib> declares the functions described in this subclause.
— end note]
int rand(); void srand(unsigned int seed);
Effects: The rand and srand functions have the semantics specified in the C standard library.
Remarks: The implementation may specify that particular library functions may call rand.
It is implementation-defined whether the rand function may introduce data races ([res.on.data.races]).
[Note 2: 
The other random number generation facilities in this document ([rand]) are often preferable to rand, because rand's underlying algorithm is unspecified.
Use of rand therefore continues to be non-portable, with unpredictable and oft-questionable quality and performance.
— end note]
See also: ISO/IEC 9899:2018, 7.22.2