Declaration of Strings
In C, strings are groups of characters enclosed in quotation marks, declared as character arrays, and terminated with a '\0' (Null character). A character uses one byte in memory, whereas a single character string requires two bytes. Strings are declared with the char data type followed by the array size in square brackets, e.g., char name[20];
Strings in C can be initialized using a character array, such as char name[8] = {'P', 'R', 'O', 'G', 'R', 'A', 'M', '\0'};. Each character occupies 1 byte of memory, though the size can vary with different computer architectures. Characters in a string are stored in contiguous memory locations. The C compiler automatically inserts a null character (\0) at the end of the string, making manual initialization of the null character optional.
You can set the initial value of a character array using a string literal. If the array is too small, the literal will be truncated; if the literal is smaller, the remaining characters are undefined. If no size is specified, the array size is set to the literal's length, including the null terminator.
Examples:
char str[4] = {'u', 'n', 'i', 'x'}; is valid but problematic because it's not null-terminated.char str[5] = {'u', 'n', 'i', 'x', '\0'}; is correct and null-terminated.char str[4] = "unix"; is problematic as it lacks space for the null-terminator.char str[] = "UNIX"; is correct as the compiler sets the appropriate size and adds the null-terminatorString constants
String constants (enclosed in double quotes) can be assigned to char pointers or copied to char arrays.
Example:
char *s = "hello";
char s[100];
strcpy(s, "hello");
Differences in Behavior
- In
char *s = "hello";,spoints to the string constant in the string constant table, making it read-only. - In
char s[100]; strcpy(s, "hello");, the string is copied into the arrays, making it modifiable. - Direct assignment
s = "hello";is not allowed for arrays and will not compile.
/* Fragment 1 */
{
char *s;
s = "hello";
printf("%s\n", s);
// Output: hello
}
/* Fragment 2 */
{
char s[100];
strcpy(s, "hello");
printf("%s\n", s);
// Output: hello
}
Display of strings using different formatting
The printf function with the %s format is used to display strings. For example, printf("%s", name); displays the entire string stored in name.
To specify the accuracy and width, such as displaying the first 5 characters within a field width of 15, use:
printf("%15.5s", name);
Including a minus sign in the format (e.g., %-10.5s) left-justifies the string:
printf("%-10.5s", name);