Question

I’m doing a program transformation from a language that allows expressions in array initializers to C99, which doesn’t.

Currently, the way I’m handling this is to create an __arrayInit function and then generate a very large number of these inside:

array[0] = x + y * z; // Sample Expression
array[1] = a / b + c; // Another
array[2] = 5; // sometimes there's a constant
...

Often there are hundreds of these individual initializations. Is there a better way of doing this that executes faster? Kudos if it compiles faster as well.

Edit: The expressions are sometimes non-constant and can have variables and function calls in them.

Answer 1

C99 allows expressions in initializer

int sarray[] = {
   [0] = x + y * z, // Sample Expression
   [1] = a / b + c, // Another
   [2] = 5, // sometimes there's a constant
};

is valid syntax.

Edit:
If it is an auto variable any expression that has a type that is assignment compatible to the base type of the array is allowed.

For arrays with static storage class (either global arrays or local arrays that are additionally declared with static) you can use constant expressions composed of:

• any type of literals such as 23, 1E-45, "hello"
• enumeration constants
• address constants of global variables or functions

Not working are const qualified variables.