Question

I have a function that needs to remove leading whitespace from a string. For some reason, this does not work:

static void remove_leading_spaces(char* line)
{  
   int i;
   for(i = 0; line[i] == ' '; i++);      //iterate through till whitespace     
   line = line + i;                      //  advance the pointer to point to
                                         //  the first non space character
}

For example, if I have a string with a single leading whitespace, the string will not be altered.

Thanks everyone the answers are correct for remove_leading_spaces!

How would I do this with a string that needs to be returned from the function that calls this function? I have been trying the same approach and I keep getting a segmentation fault? Is it the same exact concept?

Answer 1

In the function below you are passing the pointer by value.

static void remove_leading_spaces(char* line) 

Which means any change to line in the body is not reflected in the caller. You need to change your function like this:

static void remove_leading_spaces(char** line) 
{   
   int i; 
   for(i = 0; (*line)[i] == ' '; i++) { } // the ';' is a HUGE TRAP prefer { }
   *line += i;
} 

EDIT

Be careful NOT to free line after this as you would not deallocate the entire string. If the memory was dynamically allocated, you’ll need to keep a backup copy of the original pointer to safely free it.