segmentation fault in free()

I got segmentation fault when I tried to call function free. may i know what is the most likely problem?

Example of my code:

unsigned int *temp;
temp = calloc(128,sizeof(unsigned int));

free(temp);

Below is the actual code

Code:

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void countingsort2(unsigned int *occ, unsigned int *a, unsigned int length)
{
  unsigned int i, left=0, right=0, j, LCP;
  unsigned int *temp, *b=NULL, *tempa=NULL;
  void *t;

  temp = calloc(128,sizeof(unsigned int));
  //  temp = (unsigned int*) malloc (128*sizeof(unsigned int));
  t = realloc(tempa, length*sizeof(unsigned int));  // create an array which stores the char position in the string
  if (t != NULL)
    tempa = t;

  for (i=0; i<128; i++)
    {
      if (occ[i] >= 1)
    {   
      //      printf("occ[%c]%d\n",i,occ[i]);
      right = left + occ[i] - 1;  //right is the right boundary of the alphabet
      t = realloc(b, occurrence[i]*sizeof(unsigned int));  // create an array which stores the char position in the string
      if (t != NULL)
        b = t;

      for (j=0; j<128; j++) // initialise temp array               
        temp[j] = 0;

      for (j=left; j<=right; j++)  // counting the occurrences of the 3rd char belonging to a char
        {               
          if ((a[j]+1)!=filelength)
            {
              temp[(unsigned int)str[a[j]+1]&0x7F] =  temp[(unsigned int)str[a[j]+1]&0x7F] + 1;
            }       
        }

      for (j=1; j<128;j++)       
        temp[j] =  temp[j] + temp[j-1];

      for (j=(right+1); j>=(left+1); j--)
        {       
          if ((a[j-1]+1)!=filelength)
        {
          b[temp[(unsigned int)str[a[j-1]+1]&0x7F]-1] = a[j-1];   
          //          printf("a%d suffixes%d j-1:%d\n",temp[(unsigned int)str[suffixes[j-1]]&0x7F]-1,suffixes[j-1], j-1);
          temp[(unsigned int)str[a[j-1]+1]&0x7F] = temp[(unsigned int)str[a[j-1]+1]&0x7F] - 1;
        }
          else
        {
          //          printf("p%d ", j);
          b[right-left] = a[j-1];
        }   
        }
        for (j=left; j<=right; j++)       
      tempa[j] = b[j-left];
    }
      left += occ[i];
    }
  if (a[length]==filelength)
    {
      tempa[length] = a[length];
    }
 
  for (j=0; j<length; j++)  //no need to check for the last element in the array a coz there's no next element for it to compare with
    {
      //  printf("%d ", a[j]);     
      LCP = 0;
      if (GetReadBit(&str[tempa[j]]) && GetReadBit(&str[tempa[j]-1]))
    {
      if (str[tempa[j]] == str[tempa[j]-1])
        {} //handle situation 3. But situation 3 too complicated to handle
      else
        {         
          NormSit(length, &LCP,j, tempa);
        }
    }
    }   
       


  free(tempa);
  free(temp);
  free(b); 
  }

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i tried to remove the free functions and my program still got segmentation fault! why is it so?

Because your error isn't with free, it's you trashing your memory some place else.

Quzah.

Quote:

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Originally Posted by quzah

Because your error isn't with free, it's you trashing your memory some place else.

Quzah.

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Can you elaborate more on trashing memory? And do I need to free array if it is created in a function? Or when the function call ended, the array will automatically free itself?

I call this function multiple times and when I call it, dynamic array will be created in this function. Does this repeating creating of dynamic array whenever the function is called cause the segmentation fault??

Reformatted

Code:

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void countingsort2(unsigned int *occ, unsigned int *a, unsigned int length)
{
    unsigned int i, left = 0, right = 0, j, LCP;
    unsigned int *temp, *b = NULL, *tempa = NULL;
    void *t;

    temp = calloc(128, sizeof(unsigned int));
    // temp = (unsigned int*) malloc (128*sizeof(unsigned int));
    // create an array which stores the char position in the string
    t = realloc(tempa, length * sizeof(unsigned int));
    if (t != NULL)
        tempa = t;

    for (i = 0; i < 128; i++) {
        if (occ[i] >= 1) {
            //      printf("occ[%c]%d\n",i,occ[i]);
            right = left + occ[i] - 1;  //right is the right boundary of the alphabet
            // create an array which stores the char position in the string
            t = realloc(b, occurrence[i] * sizeof(unsigned int));
            if (t != NULL)
                b = t;

            for (j = 0; j < 128; j++)  // initialise temp array
                temp[j] = 0;

            // counting the occurrences of the 3rd char belonging to a char
            for (j = left; j <= right; j++)
            {
                if ((a[j] + 1) != filelength) {
                    temp[(unsigned int) str[a[j] + 1] & 0x7F] =
                        temp[(unsigned int) str[a[j] + 1] & 0x7F] + 1;
                }
            }

            for (j = 1; j < 128; j++)
                temp[j] = temp[j] + temp[j - 1];

            for (j = (right + 1); j >= (left + 1); j--) {
                if ((a[j - 1] + 1) != filelength) {
                    b[temp[(unsigned int) str[a[j - 1] + 1] & 0x7F] - 1] =
                        a[j - 1];
                    //          printf("a%d suffixes%d j-1:%d\n",
                    //              temp[(unsigned int)str[suffixes[j-1]]&0x7F]-1,suffixes[j-1], j-1);
                    temp[(unsigned int) str[a[j - 1] + 1] & 0x7F] =
                        temp[(unsigned int) str[a[j - 1] + 1] & 0x7F] - 1;
                } else {
                    //          printf("p%d ", j);
                    b[right - left] = a[j - 1];
                }
            }
            for (j = left; j <= right; j++)
                tempa[j] = b[j - left];
        }
        left += occ[i];
    }
    if (a[length] == filelength) {
        tempa[length] = a[length];
    }

    //no need to check for the last element in the array a coz there's no next
    //element for it to compare with
    for (j = 0; j < length; j++)
    {
        //  printf("%d ", a[j]);
        LCP = 0;
        if (GetReadBit(&str[tempa[j]]) && GetReadBit(&str[tempa[j] - 1])) {
            if (str[tempa[j]] == str[tempa[j] - 1]) {
            }                  //handle situation 3. But situation 3 too complicated to handle
            else {
                NormSit(length, &LCP, j, tempa);
            }
        }
    }

    free(tempa);
    free(temp);
    free(b);
}

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Care of

Code:

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indent --no-tabs --indent-level4 --k-and-r-style hello.c

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