Why doesn't struct exist after declaration inside of function? - c

Question

I've tried a lot of simple examples of this and haven't gotten any to work.
My goal is to have a function which declares a struct internally, sets the values of the struct, and then returns the struct.
struct getData(void){
typedef struct{
int count1;
int count2;
} MyStruct;
MyStruct myData;
myData.count1 = 5;
myData.count2 = 6;
return myData;
};
int main(void) {
struct myData = getData()
printf("count1: %i", myData.count1);
printf("count2: %i", myData.count2);
}
Every example I've found does something similar to this, but for some reason it's not finding my struct called MyStruct. Exact error is:
error: expected identifier or ‘(’ before ‘void’
struct getData(void){
^~~~
The error I keep getting makes me think it doesn't like the struct inside the function.

Answer 1

Your problem seems to be a confusion regarding the usage of the struct keyword. You don't do struct myData to declare a variable named myData that is of struct type, because there isn't really a struct type. What you do is struct myData <SOMETHING> to define <SOMETHING> as being a new data type named struct myData. You can then say struct myData dat;, thereby declaring that dat is a variable of type struct myData.
You're also demonstrating the same confusion at the top, where you have struct getData(void)... you're attempting to declare getData as a function returning a struct, but you'd really have to do something like struct myData getData(void) to declare a function returning type struct myData.

Answer 2

I think the more standard way to write what you're after is this, using an independent definition of the struct, and then using a pointer for the function call. As written your code seems to have some scope issues (declaring a struct typedef inside a function, hmmm...) [Incorrect->] plus I don't believe structs can be passed around that way in C, I'm pretty sure you have to use pointers. [Edit oops this is incorrect! See comments]
#include<stdio.h>
typedef struct {
int count1;
int count2;
} MyStruct;
void getData (MyStruct* myDataPtr) {
myDataPtr->count1 = 5; //note pointer access notation ->
myDataPtr->count2 = 6;
};
int main(void) {
MyStruct myData;
MyStruct* sPtr = &myData; //create pointer to struct, assign to myDaya
getData(sPtr); //pass pointer to function
printf("count1: %i \n", myData.count1);
printf("count2: %i \n", myData.count2);
}
Outputs:
count1: 5
count2: 6