c++ - When a float variable goes out of the float limits, what happens? -

i remarked 2 things:

1. std::numeric_limits<float>::max()+(a small number) gives: std::numeric_limits<float>::max().

2. std::numeric_limits<float>::max()+(a large number like: std::numeric_limits<float>::max()/3) gives inf.

why difference? 1 or 2 results in overflow , undefined behavior?

edit: code testing this:

1.

float d = std::numeric_limits<float>::max(); float q = d + 100; cout << "q: " << q << endl; 

2.

float d = std::numeric_limits<float>::max(); float q = d + (d/3); cout << "q: " << q << endl; 

formally, behavior undefined. on machine ieee floating point, however, overflow after rounding result in inf. precision limited, however, , results after rounding of flt_max + 1 flt_max.

you can see same effect values under flt_max. try like:

float f1 = 1e20;     // less flt_max float f2 = f1 + 1.0; if ( f1 == f2 ) ... 

the if evaluate true, @ least ieee arithmetic. (there exist, or @ least have existed, machines float has enough precision if evaluate false, aren't common today.)