Allocate memory for a struct with a character pointer in C

Question

I was struggling to fix a code today, then I come across something similar to:

typedef struct {
int a; 
int b; 
int c;
int d;
char* word;
} mystruct;

int main(i         


        

Answer 1

You are allocating only memory for the structure itself. This includes the pointer to char, which is only 4 bytes on 32bit system, because it is part of the structure. It does NOT include memory for an unknown length of string, so if you want to have a string, you must manually allocate memory for that as well. If you are just copying a string, you can use strdup() which allocates and copies the string. You must still free the memory yourself though.

 mystruct* structptr = malloc(sizeof(mystruct));
 structptr->word = malloc(mystringlength+1);

 ....

 free(structptr->word);
 free(structptr);

If you don't want to allocate memory for the string yourself, your only choice is to declare a fixed length array in your struct. Then it will be part of the structure, and sizeof(mystruct) will include it. If this is applicable or not, depends on your design though.