Null-Terminated Strings

By far the most common use of the one-dimensional array is as a character string.
C++ supports two types of strings. The first is the null-terminated string, which is a
null-terminated character array. (A null is zero.) Thus a null-terminated string contains
the characters that comprise the string followed by a null. This is the only type of string
defined by C, and it is still the most widely used. Sometimes null-terminated strings
are called C-strings. C++ also defines a string class, called string, which provides an
object-oriented approach to string handling. It is described later in this book. Here,
null-terminated strings are examined.
When declaring a character array that will hold a null-terminated string, you need
to declare it to be one character longer than the largest string that it is to hold. For
example, to declare an array str that can hold a 10-character string, you would write
char str[11];
This makes room for the null at the end of the string.
When you use a quoted string constant in your program, you are also creating a
null-terminated string. A string constant is a list of characters enclosed in double quotes.
For example,
"hello there"
You do not need to add the null to the end of string constants manually—the compiler
does this for you automatically.
C/C++ supports a wide range of functions that manipulate null-terminated strings.
The most common are
Name Function
strcpy(s1, s2) Copies s2 into s1.
strcat(s1, s2) Concatenates s2 onto the end of s1.
strlen(s1) Returns the length of s1.
strcmp(s1, s2) Returns 0 if s1 and s2 are the same; less than 0 if s1<s2;
greater than 0 if s1>s2.
strchr(s1, ch) Returns a pointer to the first occurrence of ch in s1.
strstr(s1, s2) Returns a pointer to the first occurrence of s2 in s1.
These functions use the standard header file string.h. (C++ programs can also use the
new-style header <cstring>.) The following program illustrates the use of these string
functions:

#include <stdio.h>
#include <string.h>
int main(void)
{
char s1[80], s2[80];
gets(s1);
gets(s2);
printf("lengths: %d %d\n", strlen(s1), strlen(s2));
if(!strcmp(s1, s2)) printf("The strings are equal\n");
strcat(s1, s2);
printf("%s\n", s1);
strcpy(s1, "This is a test.\n");
printf(s1);
if(strchr("hello", 'e')) printf("e is in hello\n");
if(strstr("hi there", "hi")) printf("found hi");
return 0;
}
If you run this program and enter the strings "hello" and "hello", the output is
lengths: 5 5
The strings are equal
hellohello
This is a test.
e is in hello
found hi
Remember, strcmp() returns false if the strings are equal. Be sure to use the logical
operator ! to reverse the condition, as just shown, if you are testing for equality.
Although C++ now defines a string class, null-terminated strings are still widely
used in existing programs. They will probably stay in wide use because they offer a
high level of efficiency and afford the programmer detailed control of string
operations. However, for many simple string-handling chores, C++'s string class
provides a convenient alternative.