Compare result of std::distance with an unsigned type

Question

Hi, I wish to compare index of an element in a std::vector to an unsigned value. If I directly compare like;

if(std::distance(...)>min_distance) // true for some

I just get a warning, but works fine. However, to get rid of the warning, if I cast min_distance to int, I do not get any comparison result (although there is)

if(std::distance(...)>(int)min_distance) // never true

What is the exact problem?

Answer 1

Try

if ( std::abs( std::distance( ... ) ) > min_distance )

std::distance returns a signed value. I am assuming you are trying to get the distance in such a way that -2 AND 2 would be considered as "2". the abs function gives you the "absoloute" value which means that whatever the sign of "n" you always get a positive value back.

Answer 2

It sounds like distance is returning a negative number in some cases. Normally it would cast the int up to unsigned and the negative number would become large enough to be greater than your condition.

In the second case you would be comparing a negative number against the small positive number cast to int.

You can test this out by printing the result from distance immediately prior to using it in the comparison.