CODEWITHSUNDEEP
csegmentation-fault
Nishith Goswami
Nishith Goswami

Reputation: 363

Segmentation Fault Point

I am writing Algorithm code for removing similar character. For Ex. If input string is "abb" Output should be "a" and for "abcddbf" string output should be "acf".

I have written some code as mentioned below but some how I am getting Segmentation Faut and I am not able to find the faulty point.

Code :

#include<stdio.h>
#include<string.h>

char *remove_adjecent_string(char *in,int count)
{
int i=0;
int j=0;
int flag = 0;
int total = strlen(in);
static char *output = NULL;

if(count == 0)
{
    output=(char *)malloc(sizeof(char)*total);
    if(output == NULL)
    {
            return NULL;
    }
    for(i=0,j=0;i<=total;i++)
    {
            if(in[i] != '*')
            {
                    output[j]=in[i];
                    j++;
            }
    }
    return (char *)output;
}

for(i=0;i<=count;++i)
{ 
    printf("In loop i  :%d count :%d \t",i,count);
    printf("Before comparition in[i] = %c , in[count] = %c \t",in[i],in[count]);
    if(in[i] == in[count])
    {
            printf("Same found in[%d]  = in[%d] = %c",i,count,in[i]);
            in[i]='*';
            flag = 1;
    }
    printf(" Next loop i = %d\n",++i);
}

printf("Before Recursion \n");
output =remove_adjecent_string(in,(count-1));
return (char *)output;
}


int main()
{
  char *input;
  char *output;
  int i=0;
  input = (char *)malloc(sizeof(char)*10);
  if(input == NULL)
  {
          return;
  }
  output=(char *)malloc(sizeof(char)*10);
  if(output == NULL)
  {
          return;
  }
  input = "abbb";
  int  count = -1;
  count=strlen(input);
  output=remove_adjecent_string(input,(count-1));
  printf("Input String = %s\n",input);
  printf("Output String = %s\n",output);

}

Help me to find out the faulty case.

Upvotes: 0

Views: 123

Answers (3)

Havenard
Havenard

Reputation: 27934

Something I detected is that remove_adjecent_string() returns a buffer (named output) containing a string, but between mallocing and populating this buffer, at no moment it makes sure its a proper null-terminated string (\0 after the last character). In fact you don't even alloc enought space for that.

Depending on the situation, this may cause your printf() to print memory garbage and even cause segmentation fault, because it will keep printing whatever is in the memory after your buffer until it finally finds a null byte lost somewhere.

Upvotes: 0

tristan
tristan

Reputation: 4332

    input = "abbb";

so input points to a const string which is not modifiable. it will segv when you try to write to it:

    in[i]='*';

add: you seem to want to copy "abbb" to input so consider using strncpy()

Upvotes: 4

urzeit
urzeit

Reputation: 2909

How to find segfaults:

  1. Add debugging symbols to your executable. If you use g++ or gcc, add the -g-option to the compiler command line.
  2. Run the program in a debugger: gdb --args ./your-program [args] for gdb and linux.
  3. Type r to run the program.
  4. Wait for the segfault to accur
  5. Type bt to print the call stack. Find the topmost line that is in your code and take the filename and line number.
  6. Have a close look at that line.

Upvotes: 0

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