Question

Given that these are allowed:

char c[] = "abc";
char c[] = {'a','b','c','\0'}
char *c = "abc";

Why then is this not allowed?

char *c = {'a','b','c','\0'};  // error: a char cannot initialize a char*

If a string literal is interpreted by the compiler as a null-terminated array of chars then I would have thought it equivalent to statement 3 above, no?

Similarly, why is this not allowed :

int arr[3];
int *i = arr; // OK
int *i = {1,2,3} // error: an int cannot initialize an int*

It’s not a huge problem, I’m just curious.. I guess the question boils down to what’s the difference between a string literal (or declared integer array) and an array of character elements when assigning to a pointer?

Answer 1

Arrays aren’t pointers. Initializing a character array with a string literal is a special case (6.7.8#14):

An array of character type may be initialized by a character string literal, optionally enclosed in braces. Successive characters of the character string literal (including the terminating null character if there is room or if the array is of unknown size) initialize the elements of the array.

and also (6.7.8#16):

Otherwise, the initializer for an object that has aggregate or union type shall be a brace-enclosed list of initializers for the elements or named members.

As to the pointer initialization (6.7.8#11):

The initializer for a scalar shall be a single expression, optionally enclosed in braces. The initial value of the object is that of the expression (after conversion); the same type constraints and conversions as for simple assignment apply, taking the type of the scalar to be the unqualified version of its declared type.