How to initialise an anonymous union within a struct in c - c

Question

I want to initialise all three arrays of mainstr , can anyone help me to initialise this anonymous union inside the struture? 0th index should initialise with interger array and 1st and 2nd indexes with char pointer.
typedef struct
{
int testy;
union
{
int a[3];
char* b[3];
}
bool testz;
} testStr;
typedef struct
{
testStr x[3];
} mainStr;
something like this,
mainStr test = {
{20, {{10, 20, 30}}, FALSE},
{10, {{"test1", "test2", NULL}}, TRUE},
{30, {{"test3", "test4", NULL}}, FALSE},
}

Answer 1

Use designators:
mainStr test = {{
{20, {{10, 20, 30}}, false},
{10, {.b={"test1", "test2", NULL}}, true},
{30, {.b={"test3", "test4", NULL}}, false},
}};
Demo

Answer 2

A bit of work, but do-able.
#include <stdbool.h>
int foo() {
typedef struct {
int testy;
union {
int a[3];
char *b[3];
};
bool testz;
} testStr;
typedef struct {
testStr x[3];
} mainStr;
testStr test1 = {20, { {10, 20, 30}}, false};
(void) test1;
mainStr test = { //
{ //
{20, { {10, 20, 30}}, false}, //
{10, { .b={"test1", "test2", NULL}}, true}, //
{30, { .b={"test3", "test4", NULL}}, false} //
}//
};
(void) test;
}

Answer 3

Some issues:
union { ... }; must end with semicolon.
Use standard bool not some home-made version.
mainStr Means there's a need for an extra pair of initializers, one for the struct, one for the array member x.
With those issues fixed, you can use designated initializers to tell the compiler which union member you are initializing:
#include <stdbool.h>
typedef struct {
int testy;
union {
int a[3];
char* b[3];
};
bool testz;
} testStr;
typedef struct {
testStr x[3];
} mainStr;
int main (void) {
mainStr test =
{
{
{20, .a = {10, 20, 30}, false},
{10, .b = {"test1", "test2", 0}, true},
{30, .b = {"test3", "test4", 0}, false},
}
};
}
It might be a good idea to use designated initializers for all struct/union members though, to get self-documenting code.