g++ 中的 const 中的存储分配

Question

I understand that c++ compilers do not usually allocate storage for a const int under certain conditions and resort to const folding. I tried out a simple program to test this:

int main()
{
    const int num = 5;
    int a[num];
}

I compiled using the -g flag and ran it in gdb. When tried to access the address of the variable num here, It showed some valid address. I did not expect this. Any insights here?

Answer 1

I understand that c++ compilers do not usually allocate storage for a const int under certain conditions and resort to const folding.

It's not clear to me whether constant folding "usually" happens, nor that the occurrence of constant folding "usually" causes the compiler to not allocate storage. The compiler will determine, somehow, whether constant folding is appropriate, and whether to allocate storage. Certain things you might do, such as passing a pointer or reference to the const object to a function, can affect its decision.

In any case, if you compile with -g , then that is definitely something that can steer the compiler toward allocating storage for the const int variable. This is the easiest way to ensure that print num in GDB actually works.