Problem with segmentation fault

Hi everyone,

I have been having trouble writing a seemingly easy program. My program must remove all white space from a string without the use of string functions or an auxiliary string.

Here is my attempt to solve this,

Code:

void removewhitespace(char *str)
{
  int i=0,j=0;
  while(str[i] != '\0'){
    if(str[i] != (' '||'\n'||'\t')){ //both characters increment
      str[j]=str[i];
      i++;
      j++;}
    else{ //if character is white space, i increments and starts replacing the white space at j.
      i++;
    }
  }
}

I get a segmentation fault on line 6. I honestly can't figure out what is causing this problem. I would think that my while statement would stop the program from accessing memory beyond the bounds of the string.

Code:

if (str[i] != (' '||'\n'||'\t'))

This does not do what you think.

It should be more like

Code:

if ((str[i] != ' ') && (str[i] != '\n') && (str[i] != '\t'))

Also, check that the input "str" is being passed into the function ok.

Use a printf statement.

Thanks for the help with that if statement. I still can't figure out why I am getting a segmentation fault though. I am debugging the program in gdb and str[i] and str[j] both print out as the first letter of my input string after I run the program once.
In case it helps, this is the program I am using to test my function,

Code:

void main(int argc, char **argv){
char *teststring = "I'm doing  great!\t\n";
removewhitespace(teststring);
printf("%s\n", teststring);
}

Try this:

Code:

char teststring[] = "I'm doing  great!\t\n";

Thank you so much, that fixed my segmentation fault problem. Why is it that the string created by a pointer doesn't work the same as a string created as an array?

I found in the C99 draft

6.7.8 Initialization #32

EXAMPLE 8 The declaration

Code:

        char s[] = "abc", t[3] = "abc";

defines ``plain'' char array objects s and t whose elements are initialized with character string literals. This declaration is identical to

Code:

        char s[] = { 'a', 'b', 'c', '\0' },
             t[] = { 'a', 'b', 'c' };

The contents of the arrays are modifiable. On the other hand, the declaration

Code:

char *p = "abc";

defines p with type ``pointer to char'' and initializes it to point to an object with type ``array of char'' with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to modify the contents of the array, the behavior is undefined.