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Initializing strings

Initializing string variables (or character arrays) with string values is in many ways even easier than initializing other kinds of arrays. There are three main ways of assigning string constants to string variables. (A string constant is a string value that was typed into the source code, as opposed to one that is generated by the program or entered by the user.)

#include <stdio.h>
#include <string.h>

int main()
{
  /* Example 1 */
  char string1[] = "A string declared as an array.\n";

  /* Example 2 */
  char *string2 = "A string declared as a pointer.\n";

  /* Example 3 */
  char string3[30];
  strcpy(string3, "A string constant copied in.\n");

  printf (string1);
  printf (string2);
  printf (string3);

  return 0;
}

1. char string1[] = "A string declared as an array.\n";

   This is usually the best way to declare and initialize a string. The character array is declared explicitly. There is no size declaration for the array; just enough memory is allocated for the string, because the compiler knows how long the string constant is. The compiler stores the string constant in the character array and adds a null character (\0) to the end.

2. char *string2 = "A string declared as a pointer.\n";

   The second of these initializations is a pointer to an array of characters. Just as in the last example, the compiler calculates the size of the array from the string constant and adds a null character. The compiler then assigns a pointer to the first character of the character array to the variable string2.

   Note: Most string functions will accept strings declared in either of these two ways. Consider the printf statements at the end of the example program above -- the statements to print the variables string1 and string2 are identical.

3. char string3[30];

   Declaring a string in this way is useful when you don't know what the string variable will contain, but have a general idea of the length of its contents (in this case, the string can be a maximum of 30 characters long). The drawback is that you will either have to use some kind of string function to assign the variable a value, as the next line of code does ( strcpy(string3, "A string constant copied in.\n");), or you will have to assign the elements of the array the hard way, character by character. (See String library functions, for more information on the function strcpy.)