How to use a struct inside another struct? - c++

Question

I want to use a nested structure, but I don't know how to enter data in it. For example:
struct A {
int data;
struct B;
};
struct B {
int number;
};
So in main() when I come to use it:
int main() {
A stage;
stage.B.number;
}
Is that right? If not how do I use it?

Answer 1

Each member variable of a struct generally has a name and a type. In your code, the first member of A has type int and name data. The second member only has a type. You need to give it a name. Let's say b:
struct A {
int data;
B b;
};
To do that, the compiler needs to already know what B is, so declare that struct before you declare A.
To access a nested member, refer to each member along the path by name, separated by .:
A stage;
stage.b.number = 5;

Answer 2

struct A {
struct B {
int number;
};
B b;
int data;
};
int main() {
A a;
a.b.number;
a.data;
}

Answer 3

struct B { // <-- declare before
int number;
};
struct A {
int data;
B b; // <--- declare data member of `B`
};
Now you can use it as,
stage.b.number;

Answer 4

The struct B within A must have a name of some sort so you can reference it:
struct B {
int number;
};
struct A {
int data;
struct B myB;
};
:
struct A myA;
myA.myB.number = 42;

Answer 5

struct A
{
int data;
struct B
{
int number;
}b;
};
int main()
{
A stage = { 42, {100} };
assert(stage.data == 42);
assert(stage.b.number == 100);
}

Answer 6

struct TestStruct {
short Var1;
float Var2;
char Var3;
struct TestStruct2 {
char myType;
CString myTitle;
TestStruct2(char b1,CString b2):myType(b1), myTitle(b2){}
};
std::vector<TestStruct2> testStruct2;
TestStruct(short a1,float a2,char a3): Var1(a1), Var2(a2), Var3(a3) {
testStruct2.push_back(TestStruct2(0,"Test Title"));
testStruct2.push_back(TestStruct2(4,"Test2 Title"));
}
};
std::vector<TestStruct> testStruct;
//push smthng to vec later and call
testStruct.push_back(TestStruct(10,55.5,100));
TRACE("myTest:%s\n",testStruct[0].testStruct2[1].myTitle);

Answer 7

I have somewhat like the following code running for a while live now and it works.
// define a timer
struct lightTimer {
unsigned long time; // time in seconds since midnight so range is 0-86400
byte percentage; // in percentage so range is 0-100
};
// define a list of timers
struct lightTable {
lightTimer timer[50];
int otherVar;
};
// and make 5 instances
struct lightTable channel[5]; //all channels are now memory allocated
#zx485: EDIT: Edited/cleaned the code. Excuse for the raw dump.
Explanation:
Define a lightTimer. Basically a struct that contains 2 vars.
struct lightTimer {
Define a lightTable. First element is a lightTimer.
struct lightTable {
Make an actual (named) instance:
struct lightTable channel[5];
We now have 5 channels with 50 timers.
Access like:
channel[5].timer[10].time = 86400;
channel[5].timer[10].percentage = 50;
channel[2].otherVar = 50000;