Problem with tacking a character from a string and replacing it with two.

PeterUK · 04-03-2014, 11:38 AM

Hi I may be asking something silly but after searching on online and playing around getting I still getting it wrong.

What I am trying to do is from a string of characters pick a one and replacing with two.

so let said you have char *string_char = "blabla'blabla";

so I have wrote something like:

Code:

char* adding_character3 (char* str)
{
	char *a;
	char *p;
	char temp = 0;
	
	for (a = p = str; *p != '\0'; ++p)
	{	  
	  if (*p == 39){
	     *a++ = 39;
	     *a++ = 39;
	  }else{
	    *a++ = *p;
	  }
	}
    *a = 0;
    return a;
    }

There is something I may be missing in term as knowledge? in the loop the following statement "a = p = str" synchronize all the address every time it increment?

The above code will give a seg fault.

What I want to is a output : "blabla''blabla"

I also try to leave "*a" out of the loop and keep loading and incrementing as it goes alone incrementing in the loop but that didnt work. What is the best way to debug "segmentation faults"?

KenJackson · 04-03-2014, 11:59 AM

Are you trying to convert a single quote ( ' ) to a double quote ( " )?
It's a different character, not two single quotes.

I haven't compiled this, but it looks right:

Code:

for (p = str;  *p;  ++p)
{	  
    if (*p == '\'')
        *p = '"';
}

ntubski · 04-03-2014, 01:38 PM

Quote:

Originally Posted by PeterUK

so let said you have char *string_char = "blabla'blabla";

You can't write to a string literal, the compiler puts them in read only pages. Add -Wwrite-strings to get warnings about this. Also, if you actually want to put 2 characters where there was 1 before, you'll need a block of memory that's one byte longer (assuming you're only working with single byte characters).

Quote:

What is the best way to debug "segmentation faults"?

Use a debugger (e.g. gdb). Often, a segfault is caused by earlier code corrupting memory, in that case tools like valgrind can be helpful too. The problem here is pretty straightforward, so there isn't need for that.

PeterUK · 04-03-2014, 03:37 PM

Quote:

Originally Posted by KenJackson

Are you trying to convert a single quote ( ' ) to a double quote ( " )?
It's a different character, not two single quotes.

Sorry the page html messed my post, as you can see 39 is a character, so that is two char where there is one, look down I have found one answer. Thanks

PeterUK · 04-03-2014, 03:39 PM

[QUOTE=ntubski;5146069]You can't write to a string literal, the compiler puts them in read only pages. Add -Wwrite-strings to get warnings about this. Also, if you actually want to put 2 characters where there was 1 before, you'll need a block of memory that's one byte longer (assuming you're only working with single byte characters).

Thanks this help, I came to that before but that went out of my head :-/. I have found one answer if you would like to give me feedback on the code it would be great. Thanks

PeterUK · 04-03-2014, 03:44 PM

Here is one way I've found how to do it and as always, I post if I think I got the answer for the threat.

here we go:

Code:

char* adding_character4 (char* str)
{

    char *p;
    int number = 0;
    int c_count_char;
    
    // find how many char " ' " is there
    c_count_char = how_many(str);
    printf ("This is value of how many = %i\n",c_count_char);
    
    number = strlen(str) + 1;
    printf ("This is value of number = %i\n",number);
    
    //adding the new space rfor the extrat char
    number = number + c_count_char;
    
    char buffer [number];
    
    p = str;
    
         int len_buffer;    
     for ( len_buffer = 0; len_buffer <= number; len_buffer++){
       
	  if (*p == 39){
	     buffer [len_buffer] = *p;
	     ++p;
	     len_buffer++;
	     buffer [len_buffer] = 39;
	    
	  }else{
	   buffer [len_buffer] = *p;
	   ++p;
	  }
    
     }
    
    puts (buffer);
    	 
  
     char *text;
     if ((text = malloc(number * sizeof(char))) == NULL) { puts("malloc unable to allocate memory"); exit(1);}
     strcpy(text, buffer);
     printf("This is the value of text =%s\n", text);
    return text;
    }

There is a function called how_many its just return the number of character I am looking for not to work with oversize buffer..etc.

Is there a better way to do this? Thanks