Question

This should be simple, but pointers to char arrays still leave me scratching my head sometimes. gcc complains that “subscripted value is neither array nor pointer” in lines 4 and 5, and “invalid type argument of ‘unary *'” on lines 8 and 11. Can someone explain what is going wrong here? I changed lines 4 and 5 to dereference the pointer first using brackets, but still can’t get what I want.

This should be a pretty simple function:

1  void makesafestr ( const char *unsafe,  const char *safe )
2  {
3    int offset=0;
4    for (; (*safe)[offset] != "\0" ; offset++) {
5      switch ((*unsafe)[offset]) {
6        case "\n":
7        case "\r":
8          *safe[offset] = "~";
9          break;
10       default:
11         *safe[offset] = *unsafe[offset];
12     }
13     offset++;
14   }
}

Answer 1

In your code safe is a pointer to a char (not a pointer to an array). So when you say *safe that’s a plain char. Instead of (*safe)[offset] try safe[offset]. Same goes for *safe[offset], same goes for unsafe.

A second problem is the way you are comparing characters. “\0” is a string literal. In your code you want a character literal. In short, the for should be:

for (; safe[offset] != '\0' ; offset++)

But you could rewrite it and make it simpler, since \0 is 0:

for (offset=0; safe[offset]; offset++)