Initialize array of char in initialization list of constructor in C++

Question

Is it ok to use initialization like this?

class Foo
{
public:
   Foo() : str("str") {}
   char str[4];
};

And this?

int main()
{
   char str[4]("str");
}

Both give me an error in gcc 4.7.2:

error: array used as initializer

Comeau compiles both.

Solution 1

This code is valid C++03 and gcc is simply not conformant here.

The language that allows this syntax for initializing character arrays is the same as allows it for any other type; there are no exceptions that would prohibit it from being used on character arrays. () and = initialization are equivalent in these cases and the character array should simply be initialized according to 8.5.2.

Here's a confirmed gcc bug report that covers this.

Solution 2

In C++03, the non-static member array cannot be initialized as you mentioned. In g++ may be you can have an extension of initializer list, but that's a C++11 feature.

Local variable in a function can be initialized like this:

char str[] = "str"; // (1)
char str[] = {'s','t','r',0}; // (2)

Though you can mention the dimension as 4, but it's better not mentioned to avoid accidental array out of bounds.

I would recommend to use std::string in both the cases.

Solution 3

In C++03, that is not possible. Comeau might compile it because of non-Standard extension.

In C++11, you can do this:

Foo() : str({'s','t','r'}) {}       //C++11 only

Or, you may prefer this intead:

class Foo
{
public:
   Foo() {}
   char str[4] = "str"; //in-class initialization (C++11 only)
};

Also, you might consider using std::string or std::vector<char> irrespective of the version of C++ you're using.