numeric_limits::max and "invalid conversion from 'int (*)()noexcept (true)' to 'value_t {aka int}'"

Question

I have a type defined using typedef unsigned int value_t; and a function

value_t find_minimal_value(...) {
    ...
    if(...) return numeric_limits<value_t>::max;
    ...
}

Compiler refuses to compile it, saying: invalid conversion from ‘int (*)()noexcept (true)’ to ‘value_t {aka int}’.

What does it mean? Looking into the numeric_limits class, the min() function should return a variable of the type passed to it via template typename, so value_t in this case. So why the code doesn't compile?

std::numeric_limits<T>::max() is a function.

Nemo
– Nemo

2014-08-26 22:34:42 +00:00
Commented Aug 26, 2014 at 22:34 — Nemo
– Nemo, Commented Aug 26, 2014 at 22:34
@Nemo This is ridiculous, thanks.

mirgee
– mirgee

2014-08-26 22:35:35 +00:00
Commented Aug 26, 2014 at 22:35 — mirgee
– mirgee, Commented Aug 26, 2014 at 22:35

David G · Accepted Answer · 2014-08-26 22:35:36Z

8

std::numeric_limits::max() is a function, so you need to return the result of its invocation. That is done using the call operator:

value_t find_minimal_value() {
    if (...) return numeric_limits<value_t>::max();
    //                                          ^^
}

The error message meant that it couldn't convert a function pointer (i.e int (*)() to unsigned int.

answered Aug 26, 2014 at 22:35

David G

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