Why do I keep getting "error: variable has incomplete type 'struct intVec'?

Question

I'm doing an assignment for my data structures class and I have very little experience with C structures and C in general. This is the .h file that I was given to do the assignment:

#ifndef C101IntVec
#define C101IntVec
typedef struct IntVecNode* IntVec;
static const int intInitCap = 4;
int intTop(IntVec myVec);
int intData(IntVec myVec, int i);
int intSize(IntVec myVec);
int intCapacity(IntVec myVec);
IntVec intMakeEmptyVec(void);
void intVecPush(IntVec myVec, int newE);
void intVecPop(IntVec myVec);
#endif

This is the .c implementation that I've made:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "intVec.h"
typedef struct IntVecNode {
    int* data;
    int sz;         // Number of elements that contain data
    int capacity;   // How much is allocated to the array
} IntVecNode;
typedef struct IntVecNode* IntVec;
//static const int intInitCap = 4;
int intTop(IntVec myVec) {
    return *myVec->data;
}
int intData(IntVec myVec, int i) {
    return *(myVec->data + i);
}
int intSize(IntVec myVec) {
    return myVec->sz;
}
int intCapacity(IntVec myVec) {
    return myVec->capacity;
}
IntVec intMakeEmptyVec(void) {
    IntVec newVec = malloc(sizeof(struct IntVecNode));
    newVec->data = malloc(intInitCap * sizeof(int));
    newVec->sz = 0;
    newVec->capacity = intInitCap;
    return newVec;
}
void intVecPush(IntVec myVec, int newE) {
    if (myVec->sz >= myVec->capacity) {
        int newCap = myVec->capacity * 2;
        myVec->data = realloc(myVec->data, newCap * sizeof(int));
    } else {
        for (int i = 0; i < myVec->capacity; i++) {
            *(myVec->data + i) = *(myVec->data + i + 1);
        }
        myVec->data = &newE;
    }
    myVec->sz++;
}
void intVecPop(IntVec myVec) {
    for (int i = 0; i < myVec->capacity; i++) {
        *(myVec->data - i) = *(myVec->data - i + 1);
    }
    myVec->sz--;
}

This is the test file:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "intVec.c"
int main() {
    struct IntVec v;
    v.intVecPush(v,0);
    return 0;
}

Every time I run the test file, I get the error:

test.c:7:16: error: variable has incomplete type 'struct IntVec'
        struct IntVec v;
                      ^
test.c:7:9: note: forward declaration of 'struct IntVec'
        struct IntVec v;
               ^
1 error generated.

I've tried changing the #include "intVec.c" to "intVec.h" in the test file, however that produces the same error. What would I need to change in order to not get this error?

Solution

There is no structure definition struct IntVec.

So the compiler is unable to define the object v

struct IntVec v;

I think you mean

IntVec v;

And this call

v.intVecPush(v,0);

is invalid and does not make sense. I think there should be something like

IntVec v = intMakeEmptyVec();
intVecPush(v,0);

instead of

struct IntVec v;
v.intVecPush(v,0);

Also it is a bad idea to include the whole module in another module. You should place the structure definition in the header and include this header in the compilation unit with main.

That is move these definitions

typedef struct IntVecNode {
    int* data;
    int sz;         // Number of elements that contain data
    int capacity;   // How much is allocated to the array
} IntVecNode;
typedef struct IntVecNode* IntVec;

in the header.

Comments

[melpomene]

Use a type that actually exists. There is no struct IntVec in your code.

[user2357112]

Also, you should be including the .h file instead of the .c file. It is extremely rare for including a .c file to be the right thing to do.

[M.M]

Change main to IntVec v = intMakeEmptyVec(); intVecPush(v, 0);. Although I would recommend not using pointer typedefs as they are confusing (it looks like your code is copying an intvec by value when in fact it is not)

[ikegami]

Code using this library will leak! (There's no way to free the vec)

[Vlad from Moscow]

@JamieNguyen As I have pointed in my answer you have to write at least IntVec v; instead of struct IntVec v;

[Jamie Nguyen]

Changing struct IntVec; to IntVec; i get: test.c:8:3: error: member reference type 'IntVec' (aka 'struct IntVecNode ') is a pointer; did you mean to use '->'? v.intVecPush(v,0); ~^ -> test.c:8:3: error: incomplete definition of type 'struct IntVecNode' v.intVecPush(v,0); ~^ ./intVec.h:11:16: note: forward declaration of 'struct IntVecNode' typedef struct IntVecNode IntVec; ^ 2 errors generated. Changing the v.IntVecPush(v,0) to v->IntVecPush(v,0) brings me back to the incomplete type error again.

[Vlad from Moscow]

@JamieNguyen See my updated post. It seems you do not understood what you are doing.