CODEWITHSUNDEEP
c
EvgK
EvgK

Reputation: 53

const in C: Cannot allocate an array of constant size 0

A small piece of code:

void func()
{
   const int BUF_SIZE = 5;
   char scale[BUF_SIZE];
}

This code is built fine under C++, but under C I have an errors:

error C2057: expected constant expression
error C2466: cannot allocate an array of constant size 0

Why?

Compiler: Microsoft Visual C++ 2008

Thanks in advance!

Upvotes: 5

Views: 4978

Answers (3)

Seth Kingsley
Seth Kingsley

Reputation: 452

Better yet, use enum { BUF_SIZE = 5 }; so that the debugger knows about it.

Upvotes: 1

Cesar Najera
Cesar Najera

Reputation: 83

I would do something like this:

#define BUF_SIZE 5
void func(){
    char scale[BUF_SIZE];
}

That will do what you need

Upvotes: 2

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272772

In C (all variants, I believe), a const is, ironically, not a constant expression in C. In pre-C99, array lengths must be a constant expression.

However, C99 has the concept of "variable length arrays", so if you're compiling with a C99-compliant compiler, your code should be valid even though BUF_SIZE is not a constant expression.

Upvotes: 5

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