Thread: problem accessing a struct member

I usually write things in C++, but I have to use C to work with this vr library, so please excuse the stupid question. I have a bunch of data allocated like this:

Code:

#define MAXWALLS 1000       //maximum number of walls

typedef struct {
    Vec pos;
    float th, w, h;
} Wall;

typedef struct {
    enum {placingWall, rotatingWall} state;

    int numBalls;
    int numWalls;

    Vec tip;
    Vec ground;
    bool goodGround;
    
    Ball ball[MAXBALLS];
    Wall wall[MAXWALLS];

    vrLock lock;

} WorldData;

And at another point in my code I want to increment the th value of a wall, which I'm doing like this (expanded into multiple lines to isolate the error):

Code:

            int index = (wd->numWalls-1) % MAXWALLS;
            Wall* wall = &wd->wall[index];
            wall->th += WALLROTATESPEED * deltaTime;   <- this line generates the error
            /*wd->wall[(wd->numWalls-1)%MAXWALLS].th += WALLROTATESPEED * deltaTime;*/

The problem is that when I try to compile this with cc, I get this error:

mp2sim.c:118: error: syntax error before ‘=’ token

I don't see what could be causing this. Is there some cryptic c thing going on here or am I declaring my structs wrong or what?

> Wall* wall = &wd->wall[index];
Don't you need the struct keyword:

Code:

            struct Wall* wall = &wd->wall[index];

Doing that just gives me a more elaborate error:

mp2sim.c:117: warning: initialization from incompatible pointer type
mp2sim.c:118: error: dereferencing pointer to incomplete type
mp2sim.c:118: error: syntax error before ‘=’ token

See if you get an error if you don't use a pointer:

Code:

            Wall wall = wd->wall[index];
            wall.th += WALLROTATESPEED * deltaTime;   <- this line generates the error

Your code compiles fine for me (it is a C++ compiler though).
Check if you have some conflicting macro. Or try to remove part by part until it compiles (meaning the last action removed the error).

It's been a long while since I programmed in pure C, perhaps it's an old compiler that doesn't allow some construct (like += operator?) or something...

you can't declare your variable mid-function. Go to the beginning of the function and declare your variable first: Wall* wall;

In C all your variables must be declared before use.