Question

I’m writing a small language in C, and it requires variable setting. I have a variable table set up, but I’m getting a strange error.

#define VAR_SIZE 100
typedef struct {
    const char *key;
    int value;
} variable;

variable Table[VAR_SIZE];
Table[0].key = NULL;
Table[0].value = 0;

When I run that, I get the following error:

stack.c:8: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘->’ token
stack.c:9: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘->’ token

What’s going on?

Answer 1

You’re trying to write code at global scope. You can’t do that. You either need to give your global variable a static initializer, or initialize it at runtime inside of a function call.

An example of a static initializer:

variable Table[VAR_SIZE] = {
    {NULL, 0},  // index 0
    {NULL, 0},  // index 1
    // etc.
};

Initializing at runtime:

variable Table[VAR_SIZE];

void init_table(void) {
    Table[0].key = NULL;
    Table[0].value = 0;
    // etc.
}

int main(int argc, char **argv) {
    init_table();
    // rest of program
}

If you’re compiling in C99 mode, you can also use a designated initializer:

// The following is valid C99, but invalid C89 and invalid C++
variable Table[VAR_SIZE] = {
    [0] = {   // initialize index 0
        .key = NULL,
        .value = 0
    },
    // etc.
};