Question

I have a struct with two pointers to functions and some data. The functions are definition-wise the same, however they should perform different tasks (which is why they have different names in the original source). If I use the first function, all goes well, but if I use the second functions, I get a segfault – even if I pass the same pointer to both functions.

The pointers are neither NULL nor garbage, or else both would fail – but somehow only the latter gets segfaulted. Why is that?

I have the following code:

typedef void (*funcOneDef)(void*);
typedef void (*funcTwoDef)(void*);
typedef struct structImpl* structPt;

struct structImpl {
    void *data;
    funcOneDef funcOne;
    funcTwoDef funcTwo;
}; 

structPt create(void *data, funcOneDef funcOne, funcTwoDef funcTwo)
{
    structPt test = malloc(sizeof(test));
    test->data = data;
    test->funcOne = funcOne;
    test->funcTwo = funcTwo;
    return test;
}

void execFuncOne(structPt test) 
{
    test->funcOne(test->data); //works!
}

void execFuncTwo(structPt test)
{
    test->funcTwo(test->data); //segfault!
}

PS: No need to test this, because somehow this works, but my original source – which is basically the same – doesn’t?

Answer 1

Shouldn’t the line structPt test = malloc(sizeof(test)); be structPt test = malloc(sizeof(structImpl));?