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# 1  
Old 11-02-2007
pointers
Hi I mash with pointers in C. I solve this problem about 5 hours and I don't know how I should continue.


Code:
void InsertFirst (tList *L, int val)   {
   tElemPtr new;
        if((new = malloc(sizeof(tElemPtr))) == NULL) Error();

   new->data = val;
   new->ptr = L->frst;
   L->frst = new;
   return;

}


and Valgrind writes this:

Code:
Invalid write of size 4
==3742==    at 0x804847C: InsertFirst (in /home/Digimon/c201/prog)
==3742==    by 0x804865E: main (in /home/Digimon/c201/prog)
==3742==  Address 0x402302C is 0 bytes after a block of size 4 alloc'd
==3742==    at 0x4005400: malloc (vg_replace_malloc.c:149)
==3742==    by 0x8048467: InsertFirst (in /home/Digimon/c201/prog)
==3742==    by 0x804865E: main (in /home/Digimon/c201/prog)
==3742==
==3742== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 13 from 1)
==3742== malloc/free: in use at exit: 0 bytes in 0 blocks.
==3742== malloc/free: 1 allocs, 1 frees, 4 bytes allocated.
==3742== For counts of detected errors, rerun with: -v
==3742== All heap blocks were freed -- no leaks are possible.


I think, that I should alocated in structure space for each element
# 2  
Old 11-02-2007
Quote:
Originally Posted by Milla
tElemPtr new;
if((new = malloc(sizeof(tElemPtr))) == NULL) Error();
1. don't use the word "new", it's a reserved word in C++ so a bit of a bad habit and may trip up some C/C++ compilers.

2. You have allocated space for the size of the pointer, not to what it points to.

Code:
   tElemPtr newElem;
        if((newElem = malloc(sizeof(newElem[0]))) == NULL) Error();
....

# 3  
Old 11-03-2007
Thanks a lot Smilie
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