What is Null-Terminated String
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.
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”
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 s1s2.
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 .) The following program illustrates the use of these string functions:
#include
#include
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.
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