C: removing extra spaces in line

[deathmetal]

Hi,
My goal is to remove extra spaces from line.

I've tried multiple ways, many variables. But I get error for seg fault.

My code:

  unsigned int j=0;                                                                                                                                                                            
  char *line="a    good";                                                                                                                                                                      
  char *temp;                                                                                                                                                                                  
                                                                                                                                                                                                                                                                                                                                                  
  while(*(line+j)){                                                                                                                                                                            
                                                                                                                                                                                               
    if(*(line+j)==' ' && *(line+j+1) ==' ' ){                                                                                                                                                  
      temp=line+j+1;                                                                                                                                                                           
                                                                                                                                                                                               
      while(*(temp)!='\0'){                                                                                                                                                                    
        *(temp-1)=*(temp);                                                                                                                                                                     
        temp++;                                                                                                                                                                                
                                                                                                                                                                                               
      }                                                                                                                                                                                        
    }                                                                                                                                                                                          
                                                                                                                                                                                               
    j++;                                                                                                                                                                                       
  }

Cannot understand my bug.
Sorry for naive problem.

[Matticus]

You're attempting to modify a string literal, which is a no-no. Using "temp" as an intermediary pointer just hides this fact.

Try changing "line" to a suitably sized array and see what happens.

I suspect you did not come up with an algorithm before writing this code, since the results are incorrect. I suggest planning this out on paper before trying to implement it in code.

[deathmetal]

You're attempting to modify a string literal, which is a no-no. Using "temp" as an intermediary pointer just hides this fact.

Try changing "line" to a suitably sized array and see what happens.

I suspect you did not come up with an algorithm before writing this code, since the results are incorrect. I suggest planning this out on paper before trying to implement it in code.

Hi Matt,
Thanks for your reply.

  unsigned int j=0;                                                                                                                                                                            
  char line[]="a    good";                                                                                                                                                                     
  char *temp;                                                                                                                                                                                  
                                                                                                                                                                                               
  while(*(line+j)){                                                                                                                                                                            
                                                                                                                                                                                               
    if(*(line+j)==' ' && *(line+j+1) ==' ' ){                                                                                                                                                  
                                                                                                                                                                                               
      temp=line+j+1;                                                                                                                                                                           
      while((*temp++)!='\0'){                                                                                                                                                                  
        *(temp-1)=*(temp);                                                                                                                                                                     
                                                                                                                                                                                               
      }                                                                                                                                                                                        
    }                                                                                                                                                                                          
    else{                                                                                                                                                                                      
      j++;                                                                                                                                                                                     
                                                                                                                                                                                               
    }                                                                                                                                                                                          
                                                                                                                                                                                               
  }                                                                                                                                                                                            
                                                                                                                                                                                               
  line[j]='\0';

If I create a function, and pass a string literal then it would fail too, I believe. Because that is my next step.

[Matticus]

If I create a function, and pass a string literal then it would fail too, I believe. Because that is my next step.

Yes. As I said, you cannot modify a string literal. You would need to pass a modifiable value to this function, such an an array or a pointer to allocated memory.

[laserlight]

A style recommendation: use line[j] instead of *(line+j). That said, I would have two pointers: one points to the current position to write, the other points to the current position to read (as in examine the value of the character to see if it is a space or not). As reading progresses, I increment the read pointer; as writing progresses, I increment the write pointer. I would also have a flag that is set whenever a space is encountered, and unset whenever a non-space is encountered, and based on this flag I can determine whether to skip a space that was just read, or to write it. With this approach, I would not need nested loops: the loop "reads" the input string character by character.