problem with malloc (77128,0x7fffb99573c0) malloc: *** error for object 0x7fd77c4025c8:

Question

I have homework to do with malloc and have an issue.

I have to take what is given as a array of string in av and put it in a structure that goes like this:

typedef struct s_stock_str
{
     int size;    // the size of the string
     char *str;   // the string
     char *copy;  // a copie of the string 
} s_stock_str;

The problem is that I count all the characters that the chain in the array have and malloc it to a pointer in this form:

lentstr = ((lentstr + ac -1) * 2 + ((ac -1 )*sizeof(int)));
pointeur = malloc((sizeof(char) * lentstr));

lentstr + ac -1 for the space of '\0'
*2 for the place of the copy
((ac -1 )*sizeof(int)) for the size of the int

and I multiply everything with the size of a char.
ac is the number of arguments and we don't use the first one so I put -1.

I malloc everything but after first argument it give me this error:

a.out(77128,0x7fffb99573c0) malloc: * error for object 0x7fd77c4025c8: incorrect checksum for freed object - object was probably modified after being freed. * set a breakpoint in malloc_error_break to debug

Could someone explain to me what is this ?

int     taille(int ac, char **av)
{
  int i;
  int a;
  int compteur;

  compteur = 0;
  i = 0;
  a = 1;
  while(a < ac )
  {
    i = 0;
    while(av[a][i++])
        compteur++;
    a++;
  }
  return (compteur);
}

struct s_stock_str *ft_strs_to_tab(int ac, char **av)
{
  s_stock_str *pointeur;
  int lentstr;
  int i;
  int size;

  lentstr = taille(ac, av);
  lentstr = ((lentstr + ac -1) * 2 + ((ac -1 )*sizeof(int)));
  pointeur = malloc((sizeof(char) * lentstr));
  i = 1;
  while (i < ac)
  {
    size = tailletableau(av[i],i);
    pointeur[i].size = size;
    pointeur[i].str = av[i];
    pointeur[i].copy = copie(av[i],size, i);
    i++;
  }   
  return pointeur;
}

I'm not quite sure what's going on with your malloc call. The sizeof operator can be applies to structs, so really it seems like you should be calling something along the lines of malloc(sizeof(struct s_stock_str) * ac) to get chunk of memory that can hold ac of the type struct s_stock_str — Clayton L
Since you trying to create an array of s_stock_str elements and index it up to the value ac-1, you should be allocating pointeur = malloc(sizeof(s_stock_str) * ac);. Also, you have not shown what the copie function does. — paddy
the copie fonction only copie src to a pointer of char and give it to the outpout :/ nothing else char copie(char *av, int size, int i) { char *copier; i = 0; copier = malloc(sizeof(*av) (size + 1)); while(av[i]) { copier[i] = av[i]; i++; } copier[i] = av[i]; return (copier); } — pikl
@ClaytonL you are a genuis , i make a sizeof the struct and it work , thank you very mush — pikl

virolino virolino · Accepted Answer · 2019-07-17T06:29:35

s_stock_str *pointeur;
...
pointeur[i].size = size;
...

You are definitely writing to unallocated memory if i > 1 (you mallocated memory for only one element).

Also, this:

i = 1;
while (i < ac)
{
  size = tailletableau(av[i],i);
  pointeur[i].size = size;
  pointeur[i].str = av[i];
  pointeur[i].copy = copie(av[i],size, i);
  i++;
}

should be written as a for (for simplicity and readability):

for( i = 1; i < ac; i++)
{
  size = tailletableau(av[i],i);
  pointeur[i].size = size;
  pointeur[i].str = av[i];
  pointeur[i].copy = copie(av[i],size, i);
}

problem with malloc (77128,0x7fffb99573c0) malloc: *** error for object 0x7fd77c4025c8:

1 Answers