Strings and Vectors

Slide 8- 5
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
An Array Type for Strings

C-strings can be used to represent strings of
characters

C-strings are stored as arrays of characters

C-strings use the null character '\0' to end a
string

The Null character is a single character

To declare a C-string variable, declare an array
of characters:
char s[11];
Slide 8- 6
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Declaring a C-string as char s[10] creates space
for only nine characters

The null character terminator requires one
space

A C-string variable does not need a size variable

The null character immediately follows the last
character of the string

Example:

??\0!moMiH
s[9]s[8]s[7]s[6]s[5]s[4]s[3]s[2]s[1]s[0]
C-string Details
Slide 8- 7
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
C-string Declaration

To declare a C-string variable, use the syntax:
char Array_name[ Maximum_C_String_Size + 1];

+ 1 reserves the additional character needed
by '\0'
Slide 8- 8
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Initializing a C-string

To initialize a C-string during declaration:
char my_message[20] = "Hi there.";

The null character '\0' is added for you

Another alternative:
char short_string[ ] = "abc";
but not this:
char short_string[ ] = {'a', 'b', 'c'};
Slide 8- 9
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
C-string error

This attempt to initialize a C-string does not
cause the \0 to be inserted in the array

char short_string[ ] = {'a', 'b', 'c'};
Slide 8- 10
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Don't Change '\0'

Do not to replace the null character when
manipulating indexed variables in a C-string

If the null character is lost, the array cannot act
like a C-string

Example: int index = 0;
while (our_string[index] != '\0')
{
our_string[index] = 'X';
index++;
}

This code depends on finding the null character!
Slide 8- 11
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Safer Processing of C-strings

The loop on the previous slide depended on
finding the '\0' character

It would be wiser to use this version in case the
'\0' character had been removed
int index = 0;
while (our_string[index] != '\0'
&& index < SIZE)
{
our_string[index] = 'X';
index++;
}
Slide 8- 12
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Assignment With C-strings

This statement is illegal:
a_string = "Hello";

This is an assignment statement, not an
initialization

The assignment operator does not work with
C-strings
Slide 8- 13
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Assignment of C-strings

A common method to assign a value to a
C-string variable is to use strcpy, defined in
the cstring library

Example: #include <cstring>
…
char a_string[ 11];
strcpy (a_string, "Hello");
Places "Hello" followed by the null character in
a_string
Slide 8- 14
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
A Problem With strcpy

strcpy can create problems if not used carefully

strcpy does not check the declared length of
the first argument

It is possible for strcpy to write characters
beyond the declared size of the array

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