C Double Pointer to Structure

Question

I am trying to work out a double pointer to a structure in C and cannot figure out what is going wrong... The simple source is below:

typedef struct {     int member; } mystruct;  void myfunc(mystruct **data) {     (*data)->member = 1; }  void main(int argc, char *argv[]) {     mystruct **data;      myfunc(data);      printf("member = %d\n", (*data)->member); } 

A similar question was asked here: How to work with pointer to pointer to structure in C? on how to modify a member of a structure through a double pointer. The solution was the syntax (*data)->member = 1; which makes sense. But in my little application here, I receive a seg fault when executing that line. What am I doing wrong?

Thanks

Answer 1

You need to point to something if you are going to dereference a pointer. Try this:

void main(int argc, char *argv) {     mystruct actualThing;     mystruct *pointer = &actualThing;     mystruct **data = &pointer;     myfunc(data);      printf("Member: %d", (*data)->member); }