c - How would I free a pointer malloc'd in a separate function? -

i have global variable called exam of type struct exam:

typedef struct  {     question* phead; }exam;  exam exam; 

in function malloc space pointer phead:

int initexam() {     exam.phead = malloc(sizeof(question*));     exam.phead = null;      return 1; } 

in separate function try free memory:

void cleanup() {     unsigned int = 0;     question* currentquestion = exam.phead;      while (currentquestion != null) {         // other code     }     exam.phead = null; } 

i have tried following inside function:

free(exam.phead); 

my issue not seem free memory allocated malloc. cleanup() free memory allocated exam.phead , cannot change function signatures or move free() calls function. there i'm doing wrong? i'm new c programming. thanks!

you have memory leak, right off:

int initexam() {     exam.phead = malloc(sizeof(question*));//assign address of allocated memory     exam.phead = null;//reassign member, null-pointer      return 1; } 

the exam.phead member assigned address of memory allocated, become null-pointer right after. null pointer can free'd safely, doesn't do anything.
meanwhile, malloc'ed memory stay allocated, have no pointer it, , therefore cannot manage it. can't free memory, nor can use it. take null assignment attempt initialize memory "clean" value. there ways to this, i'll in moment.

anyway, because phead null, following statements:

question* currentquestion = exam.phead;//is same currentquestion = null; while (currentquestion != null) //is same while(0) 

don't make sense, @ all.

to initialize newly allocated memory, either use memset, or calloc. latter initializes allocated block of memory zero, memset can (calloc same calling malloc + memset), allows initialize value like:

char *foo = calloc(100, sizeof *foo);// or calloc(100, 1); //is same writing: char *bar = malloc(100); memset(bar, '\0', 100);