C: Assigning "static const char * const" to "static const char *"

Question

I have a program with some global strings defined at the top of the file like this: ``` static const char * const STRING_A = "STRING A"; static const char * const STRING_B = "STRING B"; ``` Then in the main program loop I repeatedly call a function. This function contains a pointer which is to point to the above strings, depending on user input. By default I want it to be set to STRING_A, so what I essentially have is this: ``` // Called repeatedly from a loop. void input_function() { static const char *current = STRING_A; // Do stuff and reassign different strings to "current" ... } ``` The problem that I have is that when compiling I get "error: initializer element is not constant". This is using GCC 4.7.2. What confuses me more is that the error goes away if I get rid of the "static" keyword in the input function. This isn't a solution though, as the static keyword is needed for the function to keep track of the current string between calls. Obviously I could fix this in many ways,…

Accepted Answer

6.7.8/4 [C99]:

All the expressions in an initializer for an object that has static storage duration shall be constant expressions or string literals.

`STRING_A` is neither, hence the error.

One to way to work around this would be along the following lines:

```
void input_function()
{
    static const char *current = NULL;
    if (current == NULL) {
        current = STRING_A;
    }

...
}
```

C: Assigning "static const char * const" to "static const char *"

Solution

Problem