malloc/reallocing struct fields

[smalltreee]

Hi, need to dynamicaly create/resize a char array
which is a field in a struct. The struct is an element
in an array of structs. the code compiles ok but
the program crashes whenever I run it, i.e. doesn't
end or exit.

#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

extern int errno;


struct stuff {
    char *dave, *temp_dave;
    int steve;
};

int main() {


    struct stuff *mate=NULL, *temp_mate;


    mate=(struct stuff *)malloc(sizeof(struct stuff));
    if(mate=NULL) {
        perror("malloc\n");
        exit(1);
   }

    mate[0].dave=(char *)malloc(sizeof(char));
    if(mate[0].dave==NULL)  {
        perror("malloc\n");
        exit(1);
    }
	

    temp_mate=(struct stuff *)realloc(mate, 
                         sizeof(structstuff+sizeof(struct stuff));
    if(temp_mate==NULL) {
        perror("realloc\n");
        exit(1);
    }

    mate=temp_mate;
    free(mate[0].dave);
    free(temp_mate);
    printf("\nexit ok\n");
    return 0;
}

any ideas, or suggestions? Cos I'm all out. Any help would be greatly appreciated.

[sean345]

Here is what I did with your code. I left a note when there was error checking to be done. I did not resize the struct, but it is similiar to how I did the char* dave.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>



struct stuff {
    char *dave, *temp_dave;
    int steve;
};

int main(void) {
    struct stuff *mate = NULL;

	mate = malloc(sizeof(struct stuff));

	mate->dave = malloc(sizeof(char)*16);
	strcpy(mate->dave, "Dave");
	printf("%s\n", mate->dave);

	mate->temp_dave = realloc(mate->dave, sizeof(char)*32);
	// Error check

	mate->dave = mate->temp_dave;

	printf("%s\n", mate->dave);

	free(mate->dave);
	return 0;
}

Notice that you need to make the char* bigger then just sizeof(char). That is because you want it to hold several char's, not just one. In this case I used 16, but you can change it to any number.

- Sean

[Hammer]

>>the code compiles ok but
Hmm, it doesn't for me, did you cut/paste this? This was an obvious typo:
>>sizeof(structstuff+sizeof(struct stuff));
Did you mean something like:
>>temp_mate=realloc(mate, sizeof(struct stuff)*2);
(you probably didn't, but hopefully you see my point)

Also, this is an error:
>>if(mate=NULL)
You've used a single equals instead of a double.

[smalltreee]

Thanks for the help guys, I did find the code worked much better when I corrected the equality test