Initializer element is not a compile-time constant using C

Question

a.h

list* FunctionNamesCreate();
list* const FunctionNames = FunctionNamesCreate();

a.c

list* FunctionCreate() {
    list* FunctionNames = listCreate(sizeof(char*));
    listPushHead(FunctionNames,"s");
    return FunctionNames;
}

list is simple void* linked list structure

When I want to create FunctionNames global variable the code editor give me the following error: a.h:8:29: error: initializer element is not a compile-time constant. If I do not use the const before FunctionNames the the code editor give me the same error.

Read [*Modern C*](https://modernc.gforge.inria.fr/) and see [this C reference](https://en.cppreference.com/w/c). Your C code is against the rules of C. — Basile Starynkevitch, Jan 18 '21 at 12:49
if you show full code what you are doing with `FunctionCreate` and `listPushHead`, i can improve answer — IrAM, Jan 18 '21 at 13:00
In practice, runtime initialization should happen early in `main` — Basile Starynkevitch, Jan 18 '21 at 13:10

Vlad from Moscow · Accepted Answer · 2021-01-18T13:08:00.900

This declaration

list* const FunctionNames = FunctionNamesCreate();

is a file scope declaration with static storage duration that may be initialized by a constant compile-time expression.

From the C Standard (6.7.9 Initialization)

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

This expression

FunctionNamesCreate()

is not a compile-time constant expression. The function call evaluates at run-time.

From the C Standard (6.6 Constant expressions)

3 Constant expressions shall not contain assignment, increment, decrement, function-call, or comma operators, except when they are contained within a subexpression that is not evaluated.

There is no need to declare the pointer at a file scope. It is a bad approach moreover when you placed a pointer definition with external linkage in a header. Declare the pointer for example in main.

score 1 · Answer 2 · answered Jan 18 '21 at 12:59

1

In C language code can be only executed inside the functions. In the global scope only constant expressions can be used to initialize the variables.

Static storage objects can be only initialized using constant expressions.

answered Jan 18 '21 at 12:59

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Initializer element is not a compile-time constant using C

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