I was reading Bjarne Stroustrup’s Programming Principles and Practice Using C++ (second edition). On page 597:

double* p5 = new double[] {0,1,2,3,4};

…; the number of elements can be left out when a set of elements is provided.

I typed the code above into Visual Studio 2022, and I get red underlines saying that "incomplete type is not allowed" (same thing happens when I define p5 as a data member), nevertheless, the code compiles and runs successfully.

May I ask if it is fine to define array in such way? If so, why would Visual Studio show those red underlines…?

>Solution :

May I ask if it is fine to define array in such way?

Yes, starting from C++11 it is valid. From new expression’s documentation:

double* p = new double[]{1,2,3}; // creates an array of type double[3]

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This means in your example,

double* p5 = new double[] {0,1,2,3,4};

creates an array of type double[5]

Demo

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Note

This is p1009r2.