5

I have the following constant struct which holds function pointers:

/* module1.h */

typedef struct my_struct my_struct_t;

struct my_struct
{
   void (*funcPtr1)(void);
   void (*funcPtr2)(void);
}

extern const my_struct_t myStruct1;



/* module1.c */

#include <module1.h>

static void func1(void)
{
   // do something
}

static void func2(void)
{
   // do something else
}

const my_struct_t myStruct1 = {
   .funcPtr1 = &func1,
   .funcPtr2 = &func2
}

So far so good!

Now I want to create a constant array of the above struct and assign the function pointers from instances of the struct:

/* module2.c */

#include <module1.h>

const my_struct_t arrayOfMyStruct[] = {
   { myStruct1.funcPtr1, myStruct1.funcPtr2 },
   // ...
}

Compiler throws an error and says, that the expressions "myStruct1.funcPtr1" and "myStruct1.funcPtr2" were not constant.
What is wrong?

alk
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momjovi89
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1 Answers1

2

myStruct1 is declared with the qualifier const, but it isn't constant. Static initialization requires it to be, and arrayOfMyStruct has static storage duration.

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

You can initialize it by using the functions directly: { func1, func2 },

or take the address of the pointer: { &myStruct1.funcPtr1, &myStruct1.funcPtr2 },

in which case you will have to use a different struct type for the array:

typedef struct 
{
   void (*const *funcPtr1)(void);
   void (*const *funcPtr2)(void);
} my_struct2_t;

And syntax for calling the function has to be changed:

(*arrayOfMyStruct[0].funcPtr2)();
this
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    The first solution is not possible in my application. In fact the type of the array in module2.c is another type but it holds the same function pointer types so I used the same to explain the problem. By the second solution you mean that I have to change the struct for module2.c in that way that it handles a "pointer to a function pointer", right? But I don't want to change that actually. Isn't there any way to make the "myStruct1.funcPtr1" constant?? – momjovi89 Jul 10 '15 at 10:02
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    @momjovi89 Apart from the ways listed above. No. – this Jul 10 '15 at 10:09