当我输入输出时，一个有趣的结果

Question

I am observing an interesting result when I typecast an output:

Here is the code snippet:

int bitSize = (int)log10(1.0*16)/log10(2.0);   //bistsize = 3  it should be 4
int temp = log10(1.0*16)/log10(2.0);           //temp = 4   

Basically I want to take log2(16) which should be 4. I think my understanding of typecasting is wrong. Any suggestions?

Thanks

Answer 1

I think you are only casting the output of the first log(..) function. Put parenthesis around the entire expression:

int bitSize = (int)(log10(1.0*16)/log10(2.0));

Answer 2

Try:

int bitSize = static_cast<int>(log10(1.0*16)/log10(2.0));

One of the niceties of the new C++ casts is that they parenthesize the argument, so it's clear exactly what you're casting.