Array type has incomplete element type 'struct instruction'

Question

How do I make this struct instruction visible to struct cpu state? Like If I put cpu state struct first it doesn't work because some other arguments won't be visible to struct instruction but if I put it reverse again I have a problem.

struct  cpu_state
{
    int nextinstructionlinenumber;
    char filename[200];
    char RLO;

    struct instruction instructionlist[INSTRUCTIONLIST_SIZE];
    int instructionlistnumber;
    struct variable variablelist[INSTRUCTIONLIST_SIZE];
    int variablelistnumber;

};
struct cpu_state CPU; 


struct instruction{
    char name[LINE_CHAR_NUM];
    void(*function)(struct cpu_state* pstate, struct line* pline);
};

for the struct instruction instructionlist[INSTRUCTIONLIST_SIZE]; to succeed, the compiler must at least know the size of the struct, so it must know its definition at this point. — wildplasser
– wildplasser, Commented Sep 19, 2021 at 0:32

Tom Karzes · Accepted Answer · 2021-09-19 00:32:45Z

1

You can create incomplete structure declarations provided they are just used for pointers. For example, the following order will work. Note that I created a dummy definition for struct variable since it was absent from the post. You can replace it with whatever you like:

struct variable {
    int     dummy_val;
};

struct cpu_state;
struct line;

struct instruction{
    char name[LINE_CHAR_NUM];
    void(*function)(struct cpu_state* pstate, struct line* pline);
};

struct  cpu_state
{
    int nextinstructionlinenumber;
    char filename[200];
    char RLO;

    struct instruction instructionlist[INSTRUCTIONLIST_SIZE];
    int instructionlistnumber;
    struct variable variablelist[INSTRUCTIONLIST_SIZE];
    int variablelistnumber;

};

struct cpu_state CPU;

answered Sep 19, 2021 at 0:32

Tom Karzes

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