在头文件中使用结构[C - Linux]

Question

I tried to use an external struct but when I compile my c code I obtained this message:

subscripted value is neither array nor pointer nor vector .

Why?

messaggio.h

struct Request {
    struct {
        u_int data_len;
        float *data_val;
    } data;
    bool_t last;
};
typedef struct Request Request;

main.c

#include "messaggio.h"

int main(void){
 struct Request x;
 x.data[0] = 4.6;
 printf("%f\n",x.data[0]);
 return 0;
}

Answer 1

The x.data is a struct, so you cannot use [] with it. Maybe you want x.data.data_val[0] .

Try this code:

struct Request x;
x.data.data_len = 5; // initialize the length, use any value you need
x.data.data_val = (float *) malloc(x.data.data_len * sizeof(float));
x.data.data_val[0] = 4.6

Answer 2

x.data is a structure and not an array.

Use x.data.data_val[0] if that is what you are trying to access. However, you have not allocated any memory for data_val . I believe you are trying to assign a number to data_len and will need to allocate the memory to hold data_len values in data_val .

Answer 3

The type of struct Request#data is an anonymous struct { u_int, float } and not an array. Thus you can't use the [] operator on it.

You probably wanted to do:

x.data.data_val[0]