sending a struct to a function, previously defined with a pointer

Question

Edit: Forget it. it was another part of the code (actually the problem was a secondary element. another pointer but not allocated with malloc, just declared, so i think the memory was allocated in another place). the example now can compile.

thanks guys. im sorry for my typos but english isnt my native language(isnt a good escuse but i will try harder) .

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hi. i want to pass the some elements (in a struct)to a function but i cannot read the elements in any way(seg faults)

#define _FILE_OFFSET_BITS 64
#define _LARGEFILE_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>   
#include <netinet/in.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include "pcre.h"
#include <arpa/inet.h>
#define BUFFER 1512


typedef struct OCR {
    unsigned long int       ocr;
    struct OCR *         prev;
    struct OCR *         next;
} ip_ocr;


int sending (ip_ocr * tmp) {
    printf("%p\n",tmp); //this outpuut
    printf("%lu",tmp->ocr); // at this point i get a seg fault
    return 0;

}

int main () {
    ip_ocr * list;
    list=malloc(sizeof(ip_ocr));
    list->ocr=1;
    list->next=NULL;
    list->prev=NULL;

    sending(list);


 }    

Answer 1

It worked on my machine after a few fixes.

Include system headers:

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

Add semicolons after these lines:

printf("%lu",tmp->ocr);
return 0;

Added (unnecessary) typecast to value returned from malloc:

list=(ip_ocr*)malloc(sizeof(ip_ocr)); /* oops, not needed */

Answer 2

I think that you must have ignored a warning that the return of malloc has been taken to be an int. Your list then goes completely wrong.

• include the correct header files
• always compile with -Wall or equivalent
• improve your code until it doesn't spit out any warning at all

Answer 3

Compiling with -Werror-implicit-function-declaration and -Werror=return-type prevents these kind of things happening in C.