Where to use std::span?

Question

I want to write a function that can accept any type of contiguous buffer (e.g. std::array, std::vector, raw array, etc) from its call site. I have come up with two methods.

Method #1:

void func( int* const buffer, const std::size_t expectedTokenCount );

Here, expectedTokenCount is the maximum number of elements that will be inserted into the buffer.

Method #2:

void func( const std::span buffer, const std::size_t expectedTokenCount );

In this approach, I think that I better write the function in a way that first checks the size of the buffer via buffer.size( ) and compares it with expectedTokenCount to make sure that its capacity is greater than or equal to expectedTokenCount otherwise it throws some kind of exception. Is this a valid and safer method than the 1st method? Which one is better? Will the behavior of span and its size member function change if a vector is passed to it or will it be the same as for array?

user_2079303 · Answer

Where to use std::span?

Where-ever you would have otherwise used a pointer and a size, you can use std::span instead of the pointer and the size.

Is [#2] a valid ... method?

Sure. You did however change the constness of the pointer. You should use std::span.

Which one is better?

Each have their uses. But in most cases passing two sizes is redundant

The use of std::span is orthogonal to the change of using two sizes. You can do #1 as void(std::span) and you can do #2 as void(int* const buffer, const std::size_t buffer_size, const std::size_t expectedTokenCount).

Using std::span is generally an improvement.

Where to use std::span?

1 Answers