为什么我们在vs代码中写C++代码时不能通过一个变量来定义数组大小？

Question

Why can't we define the array size by a variable when writing C++ in vs code?

l have typed the same code shown below in Dev C++, and such declaration is supported in Dev C++.

struct student_
{
    char name[11];
    char no[11];
    int grade;
};
struct student_ stu[n]; // not supported in vs code, but supported in Dev C++

I expect such declaration to be true, but the actual result is error.

Answer 1

Variable length arrays are not and have never been a part of standard C++. Thus, the size of a statically allocated array must be known at compile time. Some compilers support this functionality as a compiler extension (GCC does for instance), but it is not something portable. Use std::vector as a replacement.

Answer 2

Arrays in C++ are static, and that's why their size needs to be known druing compile time so appropriate space can be allocated. You can initialize the size with a variable, but again that variable must have known constant value at compile time. For that you can use constexpr keyword.

In order for your example to work, n must be declared like this:

constexpr size_t n = 5;

When you directly write a number into the size initializer, that value is naturally known at compile time and thus valid as well.

Answer 3

To solve this issue, you need to select g++ compiler step 1: go to MinGw -> bin -> g++ -> press shift + right mouse button step 2: open visual studio -> go to view -> Command pallete -> search for C++ (UI) -> go to compiler path -> paste the g++ path and then scroll down and select IntelliSense mode select -> g++x64 All done!! Happy Coding