EGR 2261 Unit 9Strings and C-Strings

Read Malik, pages 490-508 in Chapter 7, and pages 550-558 in Chapter 8.

Homework #9 and Lab #9 due next week.

Quiz next week.

Chapter 7:User-Defined Simple Data Types,

Namespaces, and the string Type

string Type

• To use data type string, a program must include the header file string.

• A string is a sequence of 0 or more characters.– The first character is in position 0.– The second character is in position 1, etc.

• Strings in C++ are enclosed in "".• Binary operator + performs the string concatenation

operation.• Array subscript operator [] allows access to an

individual character in a string.3C++ Programming: From Problem Analysis to Program Design, Seventh Edition

Additional string Operations

4C++ Programming: From Problem Analysis to Program Design, Seventh Edition

Example 7-18: swap Function

5C++ Programming: From Problem Analysis to Program Design, Seventh Edition

Chapter 8Arrays and Strings

C-Strings (Character Arrays)

• Character array: an array whose components are of type char.

• C-strings are null-terminated ('\0') character arrays.

• Example:– 'A' is the character A.– "A" is the C-string A.– "A" represents two characters, 'A' and '\0'.

7C++ Programming: From Problem Analysis to Program Design, Seventh Edition

C-Strings (Character Arrays) (cont’d.)

• Example: char name[16];• Since C-strings are null terminated and name

has 16 components, the largest string it can store has 15 characters.

• If you store a string whose length is less than the array size, the last components are unused.

8C++ Programming: From Problem Analysis to Program Design, Seventh Edition

C-Strings (Character Arrays) (cont’d.)

• Size of an array can be omitted if the array is initialized during declaration.

• Example: char name[] = "John";

– Declares an array of length 5 and stores the C-string "John" in it.

• Useful C-string manipulation functions– strcpy, strcmp, and strlen

9C++ Programming: From Problem Analysis to Program Design, Seventh Edition

C-String Comparison

• C-strings are compared character by character using the collating sequence of the system.– Use the function strcmp

• If using the ASCII character set:– "Air" < "Boat"– "Air" < "An"– "Bill" < "Billy"– "Hello" < "hello"

10C++ Programming: From Problem Analysis to Program Design, Seventh Edition

Reading and Writing C-Strings

• Most rules for arrays also apply to C-strings (which are character arrays).

• C++ does not allow aggregate operations, including assignment, comparison, input, or output on arrays in general.

• But C++ does allow aggregate input and output of C-strings.

11C++ Programming: From Problem Analysis to Program Design, Seventh Edition

C-String Input

• Example: cin >> name;

– Stores the next inputted C-string into name.• To read C-strings with blanks, use get function:

cin.get(str, m+1);– Stores the next m characters into str but the

newline character is not stored in str.– If input string has fewer than m characters, reading

stops at the newline character.

12C++ Programming: From Problem Analysis to Program Design, Seventh Edition

C-String Output

• Example: cout << name;

– Outputs the content of name on the screen.– << continues to write the contents of name until it

finds the null character.– If name does not contain the null character, then

strange output may occur.• << continues to output data from memory adjacent to name until a '\0' is found.

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Specifying Input/Output Files at Execution Time

• User can specify the name of an input and/or output file at execution time:

14C++ Programming: From Problem Analysis to Program Design, Seventh Edition

string Type and Input/Output Files

• Argument to the open function must be a null-terminated string (a C-string).– If using a string variable for the name of an I/O

file, the value must first be converted to a C-string before calling open.

– Use the c_str function to convert.• Syntax: strVar.c_str()

where strVar is a variable of type string.

15C++ Programming: From Problem Analysis to Program Design, Seventh Edition