从“double”到“float”的转换需要缩小转换

Question

I have the following lines of code:

std::vector<float> qualities = { 0.5, 0.6, 0.7, 0.8 };
std::vector<float> percentages = { 0.15, 0.16, 0.17, 0.18 };

I get the error mentioned in the title for each element. Why is that?

Answer 1

You get the message because a constant of the form (eg) 0.5 is a double , and assigning a double to a float is a narrowing conversion.

To fix this, append f to each of your constants, eg 0.5f .

Answer 2

conversion from 'double' to 'float' requires a narrowing conversion

I get the error mentioned in the title for each element. Why is that?

Because you are constructing a vector of floats using double literals. Such conversion is narrowing.

That said, such conversions are allowed in this context and the example is well-formed and should compile. I suspect that you've used some compiler options to ask the compiler to not compile some well-formed programs.

You can write a float literal by appending f to a double literal.