...
- do not need to set
errnoon an error; - have have undefined behavior if the value of the result cannot be represented (before C23; in C23 and later, their behavior is defined by the
strto*()functions); - return 0 (or 0.0) if the string does not represent an integer (or decimal), which is indistinguishable from a correctly formatted, zero-denoting input string.
...