Accessing a struct with an array of structs variables

Question

I want to make a Struct of an array of structs.I tried to change one of the structs field variables of the array of structs.Node( [Node(1,[]) | | | ] )** I don't understand why my struct array hope first node count isn't equal to 1. When I printf("%d\n",start->innercount); I expect 1 because my node1 fields innercount has been initialized to 1 and I have initialized hope struct fields to 3,node1,1.0 .

#include <stdio.h>

struct Mynode {
    int innercount;
    char token[20];
};

struct MyData {
    int count;
    struct Mynode hope[20];
    float average;
};

int main(){
    struct Mynode node1[1] = {1, "helo"};

    struct MyData data[1] =  {3, node1, 1.0};
    struct MyData* ptr = data;
    struct MyData* endPtr = data + sizeof(data) / sizeof(data[0]);
    while ( ptr < endPtr ){
        struct Mynode* start = ptr->hope;
        struct Mynode* end = ptr->hope + sizeof(ptr->hope) / sizeof(ptr->hope[0]);
    while(start < end){
        printf("%d\n",start->innercount);
        start++;
    }
    ptr++;
}
    return 0;
}

Antti Haapala · Accepted Answer · 2018-03-18 18:44:39Z

You cannot initialize an array with an array like this. Instead, the C89-style initializer expects you to spell out all the fields of the aggregate . Check your compiler output and warning settings. Specifically:

% gcc strcut.c
strcut.c: In function ‘main’:
strcut.c:15:30: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
 struct MyData data[1] =  {3, node1, 1.0};
                              ^~~~~
strcut.c:15:30: note: (near initialization for ‘data[0].hope[0].innercount’)

I.e. the node1 is used to initialize data[0].hope[0].innercount which is an integer.

The warning from GCC explains it very clearly.

Now, to initialize this I believe in C99+ you could use

struct Mynode node1[1] = {{1,"helo"}};     
struct MyData data[1] = {{3, {[0] = node1[0]}, 1.0}};

at least it works for me. However I am not sure if it is standards-compliant. In C89 you'd have to initialize the inner structure in place

struct MyData data[1] = {{3, {{1, "helo"}}, 1.0}};

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