Compare string literal vs char array

Question

I cannot find a similar answer to this.

  char buffer[] = {'a', '0'};
  char p2[] = "a";
  printf("%d", buffer==p2); // prints 0

How do I do this comparison? Is this a similar question? How do i compare a string literal to a char array.

char buffer[] = {'a', '0'};
printf("%d", buffer=="a"); // prints 0

The above are just examples, but I really need this:

 char buffer[] = {'e','a','b','g','e','l','e','g','o','n','\000','p','k','n','m','l','\000','j', 'i', 'h'};
printf("%d", buffer=="eabgelegon\000pknml\000jih");

I cannot use any other functions.

Answer 1

Arrays (or strings) in many circunstances, are converted to the address of their first element.

In your code, inside the printf(), these addresses are being compared.

To compare the stuff pointed to by the addresses you need strcmp() (for real strings) or memcmp() (for binary data)

char buffer[] = {'e','a','b','g','e','l','e','g','o','n','\000','p','k','n','m','l','\000','j', 'i', 'h'};

int equal1 = memcmp(buffer, "eabgelegon\000pknml\000jih", 20);
printf("%d", equal1);
int equal2 = memcmp(buffer, "eabgelegon\000XXXXXXXXX", 20);
printf("%d", equal2);

int equal3 = strcmp(buffer, "eabgelegon\000pknml\000jih");
printf("%d", equal3);
int equal4 = strcmp(buffer, "eabgelegon\000XXXXXXXXX");
printf("%d", equal4);

Answer 2

None of OP's 3 buffer are best described as C strings. Simply arrays of char.

char buffer[] = {'a', '0'};  // No terminating \0
char buffer[] = {'a', '0'};  // No terminating \0
// No terminating \0 yet has embedded \0
char buffer[] = {'e','a','b','g','e','l','e','g','o','n','\000','p','k','n','m','l','\000','j', 'i', 'h'};

Since OP "cannot use any other functions" ...

Find range of valid indexable memory buffer and p2. The valid indexable range of buffer is 0 to sizeof(buffer) - 1.

The same for p2 (the string literal) is complicated. If p2 was a typical C string, the range is 0 to strlen(p2) + 1. But a string literal such as "eabgelegon\000pknml\000jih" has embedded '\0' in it (as well as a terminating '\0'), so its range cannot be determined at run time with strlen(), but only at compile time with sizeof().

Let's assume the comparison should not include the string literal's terminating '\0'.

 char buffer[] = 'e','a','b','g','e','l','e','g','o','n','\000','p','k','n','m','l','\000','j', 'i', 'h'};
 char p2[] = "eabgelegon\000pknml\000jih"; // matches
 //char p2[] = "eabgelegon\000pknml\000ji "; // fails
 //char p2[] = "eabgelegon\000pk ml\000jih"; // fails

 size_t buffer_size = sizeof(buffer);
 size_t p2_size = sizeof(p2);
 // p2 should be 1 longer than buffer due to its terminating \0
 if (buffer_size + 1 != p2_size) return NOT_EQUAL; 

 size_t i;
 for (i=0; i<buffer_size; i++) {
   if (buffer[i] != p2[i]) return NOT_EQUAL;
 }
 return EQUAL;

Note: sizeof() is not a function in C, but an operator.

Answer 3

If you don't recognize it:

char buffer[] = {'a', '\0'};
char p2[] = "a";

buffer and p2 are exactly the same. With buffer you declare a character array and assign the first character as 'a' and then an explicit null-terminating character '\0' giving you a string "a". With p2 you assign the string literal "a" and the null-terminating character is automatically appended to the end. Either way -- you get the same thing, buffer and p2 hold the string "a".