Vfrdtyky

I am struggling with dynamic memory allocation. I can't see any mistakes but still get segmentation fault. Any comments on how i can improve my code are welcome.

 char* balanceStatements(char* lst) 

       {

        <some code>

        char** bad = malloc(sizeof(char*)); // the list of the bad parts of char* lst 

        char* badOrder = &lst[0]; // the pointer to the first character of the part in lst

        <some code>

              bad = includeOrder(badOrder, bad);

includeOrder:

char** includeOrder(char* order, char** list)

{

static int i = 0;

list = realloc(list, sizeof(list) + sizeof(char*)); //allocation of memory for a new pointer in the list

list[i++] = order; 

printf("vad %cn", list[0][0]);

return list;

}

the input that causes segfault is ""ZNGA 1300 2.66, CLH15.NYM 50 56.32 B, OWW 1000 11.623 B, OGG 20 580.1 B", the first part of it (ZNGA 1300 2.66) is bad, the parts are splitted with ','. This input "GOOG 300 542.0 B,AAPL 50 145.0 B,CSCO 250.0 29 B,GOOG 200 580.0 S", with the part "CSCO 250.0 29 B" being bad, does not cause the segfault. So is the cause of segfault in the improper memory allocation? If so how it should be done properly?

full code:

#include <stdlib.h>

#include <string.h>



// result will be freed

char** includeOrder(char* order, char** list)

{

static int i = 0;

list = realloc(list, sizeof(list) + sizeof(char*)); //allocation of memory for a new pointer in the list

list[i++] = order; 

printf("vad %cn", list[0][0]);

return list;

}







char* balanceStatements(char* lst) {

char type = 0;

double buy = 0;

double sell = 0;

int i = 0;

char tempQ[100] = {};

char tempP[100] = {};

char** bad = malloc(sizeof(char*)); // the list of the bad parts of char* lst

int nword = 0;

int k = 0;

int j = 0;

int isComma = 0;

char* badOrder = &lst[0]; // the pointer to the first character of the part in lst

printf("badOrder1 %c", badOrder[0]);

char* res = malloc(1000*sizeof(char));

res[0]="A";

while (lst[i]!='')

  {

  printf("char %cn", lst[i]);

  if (lst[i] == ',')

    {

    printf("bbbb");

    if (nword != 3) 

      {

      printf("bad order 2 %cn", badOrder);

      bad = includeOrder(badOrder, bad);

      printf("asdan");

      }

    printf("aaaa");

    if (isComma) 

      {

      if (type == 'B') buy += atoi(tempQ) * atof(tempP);

      else sell += atoi(tempQ) * atof(tempP);

      }

    printf("sssss");

    nword = 0;

    badOrder=&lst[++i];

    isComma = 0;

    k = 0;

    j = 0;

    }

  if (lst[i] == ' ') 

    {

    nword++;

    i++;

    }

  if (nword == 0) i++;

  if (nword == 1)

    {

    if (lst[i]>'9' || lst[i]<'0')

      {

      printf("bad ordern");

      bad = includeOrder(badOrder, bad);

      printf("svad %cn", bad[0][0]);

      while(lst[++i]!=',');

      }

    else

      {

      tempQ[k++] = lst[i++];

      }

    }



  if (nword == 2)

    {

    tempQ[k] = '';

    printf("tempQ %sn", tempQ);

    if(lst[i] == '.') isComma = 1;

    printf("asdn");

    if ( (lst[i] > '9' || lst[i] < '0') && lst[i] != '.')

      {

      includeOrder(badOrder, bad);

      while(lst[++i]!=',');

      }

      else

        {

        tempP[j++] = lst[i++];

        printf("lst %c tempP %cn", lst[i-1], tempP[j-1]);

        }

    }

  if (nword == 3)

    {

    tempP[++j] = '';

    printf("tempP %sn", tempP);

  //  sell

    //fill in

    if (lst[i] != 'B' && lst[i] !='S')

      {

      includeOrder(badOrder, bad);

      while(lst[++i]!=',');

      }

    type = lst[i++];

    }

 /* if (nword == 4)

    {

    includeOrder(badOrder, bad);

    while(lst[++i]!=',');

    } */

  }

if (type == 'S')

  {

   sell += atoi(tempQ) * atof(tempP);

  }

  else

    {

    buy += atoi(tempQ) * atof(tempP);

    }

i=0;



  // your code

printf("buy %fn", buy);

printf("sell %fn", sell);

printf("bad %cn", bad[0][0]);

int n = 0;

while (*(bad + n))

{

n++;

}

n--;

printf("size %in", n);

while (bad[0][i]!=',' && bad[0][i]!='')

  {

  printf("%c", bad[0][i++]);

  }

sprintf(res, "Buy: %i Sell: %i", (int)buy, (int)sell);

if (bad) 

  {

  res[strlen(res)]=';';

  strcpy(&res[strlen(res)], " Badly formed ");

  res[strlen(res)] = n+48;

  res[strlen(res)] = ':';

  res[strlen(res)] = ' ';

  int i = 0;

    while ( bad[0][i] != ',' )

    {

    res[strlen(res)] = bad[0][i++];

    }

  res[strlen(res)] = ' ';

  res[strlen(res)] = ';';

}

return res;

}

The most obvious error that will crash this program is in this line:

list = realloc(list, sizeof(list) + sizeof(char*));

sizeof() is a compile time operator (except for variable lenght arrays (VLA), but these are not here), that returns the size in bytes of the type of the argument. So sizeof(list) return the size of a char**, not the allocated size of the object. There is not a function that returns the allocated size of a dynamic memory block in C, you have to keep track of that yourself, in an additional variable.

char** includeOrder(char* order, char** list, size_t *list_len)

{

    list = realloc(list, *list_len + sizeof(char*));

    ...

    return list;

}

And then in the main function:

size_t list_len = sizeof(char*); //0 is also valid

char** bad = malloc(list_len);

...

bad = includeOrder(badOrder, bad, &list_len);

Now that you are into pass-by-pointer functions you could do the same for the list variable:

void includeOrder(char* order, char*** list, size_t *list_len)

{

    *list = realloc(*list, *list_len + sizeof(char*));

    ...

}

Your problem is a misunderstanding of sizeof(list). sizeof returns the memory size of list, i.e. the size of a char**. It doesn't take into consideration the number of elements in your list.

Keep in mind that sizeof isn't a function that is executed during runtime. It is a compile time unary operator.