String

1
String

• CGS 3460, Lecture 34
• Apr 5, 2006
• Hen-I Yang

2
Previously

• Dynamic Allocated Arrays
• Dynamic Allocated Strings
• Strings

3
Agenda

• Strings

4
Strings

• String an array of characters
• String constant (String literals)
• String variable

5
String Literals

• A string that has fixed constant value, e.g. Go
  Gators!
• \ or separate double quotation can be used
  to split string literals into multiple lines
• Null character \0 at the end of each string
• Dont get confused between string literal a and
  character constant a.
• Behind the scene
• printf(abc) is handled as
• char literal abc
• printf(literal)

6
String variables

• char strSTR_LEN1
• any char array
• end with \0 (null character)
• difficult to know the length before hand, and
  hard to differentiate between char array and a
  real string
• why STR_LEN 1?

7
String variables (II)

• Initialization
• char location20 Gainesville Airport
• char location20 G,a,i,n,e,s,v,
  ,i,l,l,e, ,A,i,r,p,o,r,t,
  \0
• Like any other arrays, if length of the variable
  is less than 20, well fill them up with \0
• Initialization string cannot be longer than the
  size of the string declared
• if you declare char location Gainesville
  Airport and not specify its size, can you
  change the size later? No
• we can also declare char location array and
  pointers are closely related, but are not always
  interchangeable (e.g. location cannot point to
  somewhere else in array version)
• Always allocate memory before you use the dynamic
  pointer version

8
Reading of Strings

• char str Clock strikes 12
• printf(The message s\n, str)
• we can put the length in the conversion
  specifications
• Another way puts(str)
• no conversion specifications,
• always ends with new line

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Writing of Strings

• char str20
• scanf(s, str)
• Do we need ?
• Whitespaces
• Automatically filled with \0 at the end
• Problem with reading a whole line
• User input Clock strikes 12
• scanf will get only the word Clock
• gets(str) can actually get the whole line
• Problem of overflown
• You can write your own input functions to best
  fit your need
• read_line example on page 249
• getchar()

10
String Library

• What is a library?
• include ltstring.hgt
• char strcpy (char s1, const char s2)
• char str1 abcd
• char str2 (char ) malloc (5)
• strcpy(str2, abcd)
• char strcat(char s1, const char s2)
• strcpy(str1, efg)
• char strcmp(const char s1, const char s2)
• How to they compare?
• size_t strlen(const char s)

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String idioms

• Self-Study
• Counting the length of a string (observe how the
  code can be made compact)
• Attach a string at the end of another string

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Array of Strings

• How to store it?
• 2-D arrays or array of pointers
• Command-Line Arguments
• main(int argc, char argv)
• char Argv0 HW5
• char Argvgt0 arguments
• Argc is the length of char pointer array Argv

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By Popular Demand

• Sample Code
• Sample Code for Strings

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Summary

• Strings

15
Before you go

• Read Chapter 13
• Exercise 13.1, 13.2, 13.3, 13.9, 13.11
• Homework 5 submission on April 11, Tuesday at
  1159 pm