remove all spaces from a line in C

xeon123 · 10-22-2007, 07:32 PM

I'm trying to remove all white spaces include in a line.

for ex.
From this: " a b g f "
Become: "abgf"

Here is my code:

Code:

void trim( char* src )
{
  char *dst = src;

  while (*src != 0) {
    if (*src != ' ')
      {
          *dst++ = *src; // copy
      }

    src++;
  }

  *dst = 0;
}

The problem is that, I'm always receiving SIGBUS error and I don't know why.

1 - What am i doing wrong?
2 - Is there a form of get more detail about the causes of the error during the execution?

Thanks,

dmail · 10-22-2007, 07:37 PM

check the length of the string and how many iterations of the while loop occur.
Do you have a C programming reference book as you seem to be having a few problems with pointers at the moment.

xeon123 · 10-22-2007, 07:39 PM

The SIGBUS occur when executing:
*dst++ = *src; // copy

I don't know why.

dmail · 10-22-2007, 07:41 PM

http://en.wikipedia.org/wiki/Segmentation_fault

xeon123 · 10-22-2007, 07:42 PM

I've debugged the code, and the pointers points to the right thing.

dmail · 10-22-2007, 07:46 PM

Quote:

while (*src != 0)

Quote:

check the length of the string and how many iterations of the while loop occur.

This is not doing what you may think, try *src != '\0'

xeon123 · 10-22-2007, 07:47 PM

Ie, the pointers point to the same value.

The reason for this error, it's because, pointer dst is setting the same value as src pointer points.

Is there another way to remove all black spaces without errors?

turbo_spool · 10-22-2007, 08:03 PM

Quote:

Originally Posted by pedrosacosta

The SIGBUS occur when executing:
*dst++ = *src; // copy

I don't know why.

dst is a copy of a pointer (src) to some char.

*dst dereferences dst so that it is saying 'the actual memory that dst is pointing to'. Without the * dst is just 'the memory address of a char'. At the beginning of your routine you have:

char *dst = src;

Then later:

*dst++ = *src;

That says 'put whats at src (which can be the same exact location as dst) into dst'. This causes a memory error. Better understanding of pointers and memory locations will help you.

I always say the best book to understand using pointers in the C language is the one written by its creator: Kernighan & Ritche's 'The C Programmming Language'.

Hope this helps.

P.S. This is one of the reasons people shy away from C in certain situations. C doesn't hold your hand. As you found you, your code compiled just fine, but then bombed out with a memory error.

Welcome to the world of dynamic memory allocation.

turbo_spool · 10-22-2007, 08:17 PM

Well, by the time I posted that, you found the answer.

To answer the next question, it depends on the situation.

For example:

Code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
  char *message = "This is a null terminated string.";

  char *new_memory = malloc( sizeof(message) );
  char *pointer = new_memory;
  while (*message != (char)NULL)
  {
    if (*message != ' ')
    {
      *new_memory++ = *message;
    }

    message++;
  }
  *new_memory = '\0';
  printf("%s\n", pointer);

  pointer = NULL;
  free(pointer);
  return 0;
}

When I compile and run this I get:

Thisisanullterminatedstring.

I put it all in a main function since it was a one off specific example. I hope this helps, but again I must recommend a good book like The C Programming Language to truly get going on the subject. I just wanted to help get you going.

Also, this does not perform explicit error checking, which you should always do. For instance:

Code:

char *memory = malloc(SIZE);
if (memory == NULL) {
  // handle memory allocation error
}

Have fun!

dmail · 10-22-2007, 08:29 PM

My C is rusty and I'm sorry I have posted incorrect information.

[edit]
Your code is valid, the problem is arising due to the string being in a read only section of memory( ie on the stack).

I still prefer while (*src != '\0') to while (*src != 0) though

PAix · 10-22-2007, 08:46 PM

I hope this helps

Quote:

The C Programming Language, 270 pages,
by Brian W. Kernighan and Dennis M.Richie, 2nd Edition,
Published by Prentice Hall
ISBN 0-13-110362-8 (paperback)
ISBN 0-13-110370-9

xeon123 · 10-23-2007, 01:28 AM

turbo_spool, your code fine.

But the problem, is that, If I put you code inside a function, the malloc that you do, remove the space memory at the exit of the funcion.

Code:

void remove(char* message, char* new_memory)
{
 char *new_memory = malloc( sizeof(message) );
  char *pointer = new_memory;
  while (*message != (char)NULL)
  {
    if (*message != ' ')
    {
      *new_memory++ = *message;
    }

    message++;
  }
  *new_memory = '\0';
  printf("%s\n", pointer);

  pointer = NULL;
}

xeon123 · 10-23-2007, 01:29 AM

Please replace,
char *new_memory = malloc( sizeof(message) );
for
new_memory = (char*)malloc( sizeof(message) );